First of all, if you live under a rock and has no clue whatsoever on what I'm talking about, read it here
http://www.elderscrollsonline.com/en-gb/news/post/2016/06/12/matt-firors-message-from-be3
Secondly, I know there are other threads on the matter, but I tend to write long walls of text so I thought I should rather start a new thread with my thoughts on it.
Ok, without further ado... Let's talk about One Tamriel!
One Tamriel is EXCITING!
Right, so... Before I go into what makes me worried, let me say that I'm also excited. And I mean it! One Tamriel is the game I (and many others) always wanted - the freedom to go anywhere, to mingle with people from other factions and adventure together, to have no chains or restraints telling you what you can or can not do! This is the kind of freeform experience that many people expected from ESO since it was launched. The freedom to open up your map and say "Ok, where shall we hit next?"
This is awesome! To be able to quest and explore and venture everywhere, it's really cool. Also, some regions will make much more sense now - like Wrothgar, Gold Coast, Hew's Bane... Craglorn! (Perhaps it will be fun now?) and especially Coldharbour. For me - since launch - it was a shame that Coldharbour was not shared between the three alliances. It would make sense, gameplay and lorewise, to have folks from all three alliances working together there.
So, yay! This is promising!
But...!
Not all that glitters is gold, a very wise man once wrote...
One Tamriel is SCARY!
I'm aware that we do not have enough information yet - but I think that a big E3 announcement is enough for us to conclude that these are more than just plans already -
they are happening right now - and the sooner we make some things clear... the better! I don't claim to speak on behalf of a whole community, of course, but after a few conversations here and there I'm sure a lot of people see things in a similar fashion. And as a community it is important that we shed light upon all viewpoints so we can talk things through and build a better game
together, don't you think, ZOS?

Most of my fears are all focused on the same thing, actually: narrative. ESO has been (so far) very successful in creating memorable, immersive narratives and characters. And I must admit that you guys have some really good skills in "continuing" those stories over new content. I mean - just look at all the build-up for Darien's storyline. The new awesome dialogue with Gabrielle Benele in Anvil. The new apparitions of "old friends" with tons of great dialogue that is only made possible because of the narrative and the stories we've been playing so far. So, it is lovely to play through a whole faction's story and regions and see all the dots connecting, all the characters evolving, the Skald-King overcoming his fears, Queen Ayrenn proving herself worthy of her crown, High-King Emeric facing his own ghosts, etc... It's awesome to meet the people we've met before in other quests, see how they are doing now - what changed in their lives, etc... - all these things are great.
And with all that in mind, here's a list (literally) of all the things concerning me:
REPUTATION
There's no numerical measurement of our reputation with different factions and entities in ESO. This is usually handled by the point in the story which you'll (in theory) be there doing that. For example, you usually start your first quests as a random "no-one", all the starter zones are regions where your character is mostly unknown and you then start to earn some respect among the faction you found yourself within after escaping Coldharbour. You usually leave the first zones as someone that ascended into the "ranks" of said faction, you become the hero of Davon's Watch, you save King Casimir of Daggerfall, you become an Eye of the Queen, etc... This is completely done through dialogues, immersion, narrative. There are no measurements of reputation and therefore no "negative" reactions. When you get to Riften, you're known as the King's Arrow - because you most likely passed through that experience (of becoming the King's Arrow by completing the Eastmarch storyline), people even greet you as the King's Arrow and all that.
If I'm allowed to quest anywhere and in any order I want, all the narratives will be disrupted and make no sense. I can go to Malabal Tor where I'm a great friend of Ayrenn and then back to Auridon where I'm unknown to her. How will the game handle this?
Will all the regions and storylines be reworked to allow this kind of rupture? Or will the game's immersive and great narrative be butchered for the sake of gameplay freedom?
STORYLINES
Just like the statement above, but regarding the regional storylines. I can see that being a smaller concern - most regions have their own storyline that is usually just loosely linked to the other regions. Let's say... the vampire crisis in Rivenspire is a story of its own (and a great one at that!) and the region can certainly be played in any order and it would make sense. However there are some instances where the regional storylines do connect and form a major narrative. The whole Aldmeri Dominion storyline recaps itself over and over - being the continuous journey of Ayrenn to gather support - and there are several mentions of Estre as a dead traitor (for example) on later regions that would make no sense if you don't even played Auridon first. What about the Pact fighting together in the Rift only to go back to Eastmarch where it is being formed? And all the other cases around the game. Once again the question is the same: will the great narratives and stories of ESO be butchered for that?
ALLEGIANCE
Over the course of the game, you "kind of" pledge your allegiance to different factions and sides on the war. For example, you clearly work for each Alliance, you become an agent of the Queen in the Dominion, you work with the Pact military in the Pact and even act as some kind of personal confidant/champion to Emeric in the Covenant. This allegiance always reflected your chosen alliance - which will still "function normally" in PVP - and we always had the excuse of just being experiencing "How it would have been" in Cadwell's Silver and Gold - and never simultaneously. But now that players would have the freedom to go anywhere, how could that work? One could literally work for the three factions simultaneously without any real consequence. This kind of trivializes the idea of the three alliances, and just turns all their stories and quests into random, generic "Fetch" or "slay" quests. I mean, I'm not really a Queen's Eye, am I? I can just go to Eastmarch and become the hero of the Pact. Hooray!
TRAVEL & EXPLORATION
There's no other possible way for players from one faction to travel to another faction's territory if not by Wayshrine. And that scares me because when you start, you have this amazing feeling of a huge, living world that you can explore but you have to start from there - from where you are left. This happens naturally when you can only explore your own faction - and all the places we know and go to, all our journeys started from that single point where we were in the beginning. Now, giving players access to the other factions right off the bat by giving them access to their wayshrines across the continent would trivialize and ruin this sense of exploration and discovery. You don't have to "walk" to places - you can just teleport to the other side of the world. I honestly see only one way to make this less "impacting": to create a network of ship travels (NPCs, like we do now for some areas) that connect the different factions in a more... travel/immersion friendly way. Of course, once they are there, they discover the Wayshrines and everything works just like it does now - but getting there for the first time should require a boat travel or something like that. - giving wayshrines all across Tamriel to a new characters would just look so disencouraging
THINGS PEOPLE WILL MISS
I have this friend who recently started playing and before getting his first character to level 20, he went to Wrothgar and now The Gold Coast. This is great - and I love the fact that people have the freedom to do so. But, for obvious reasons, he "lost" a lot of great dialogues and (re)encounters with characters and stories he doesn't know yet. This will become the norm, I'm afraid. But more important than that is - will the content be retroactively updated?
What I mean is: for example, we have Raynor Vanos and his sister in The Gold Coast. If I meet them in the Pact for the first time and then I meet them in the Gold Coast, they will recognize me and treat me as an old friend. Awesome! But if I meet them in the Gold Coast first and then I meet them in the Pact regions, will they have updated dialogue for the old Pact quests? Or will we just witness an awkward Raynor that suffers from amnesia and will not recognize you? Like I said above, ZOS has always delivered AMAZING connections between characters and storylines - and opening everything up for everyone, anytime, will completely mess up logic. The more content is released, the more complex and deep the "webs" of possibilities will become. For most stories and characters to keep making sense, they'll have to be constantly updated and have new dialogue added so they can "support" their other appearances around the world. And all that will lead to an unending and confusing vortex that will result in one out of 3 things: 1- things will simply get messy and nonsensical, ruining the characters, their stories and the immersion. 2- ZOS will have a lot of trouble and effort keeping everything consistent - which is unlikely because it's a garganthuan effort, really. 3- To not "mess up", it will be easier to just make new original characters for each piece of content that we will never meet again. Boooooring.
Well, all in all, I think I've covered most of my points. Can't remember now if there was anything else. But as you can all see, it all floats around the same thing - something that has been the strongest, most important "pillar" in ESO and what it makes it so different and amazing for me: how the whole world is connected and living and immersive, how all the stories make sense and connect to each other and work really well in delivering an amazing experience that combines a great gameplay with an even greater game world.
This IS an Elder Scrolls Game, and problems aside, the living world is what makes it so. My fears is that a simple "opening" of all the factions to everyone, a simple "removal" of all the level restrictions over content and all that will, of course, bring another element from the Elder Scrolls games into ESO (Freedom)... but at which cost?
Is it really worth it?
What will we be losing, throwing away for the sake of that?
So, I don't like to finish posts on a "pessimist" note, so I'll point out 3 possible ways things could be done. Of course, as stated before, we have no information yet to know how things will work. But it's best to start talking about them sooner than later.
- The WORST possible scenario: That's it. Exactly what's promised: Level restrictions removed, faction restrictions removed, all factions sharing the same maps but no changes whatsoever. Chaos ensues, all the issues aforementioned become a reality, the game grows and attracts more players but loses all the immersion and amazing narratives and connections it once had. It becomes a formless blob of fragmented stories that barely have any context to them except for the fact that you seem to be important somehow to people you don't even know for reasons you probably don't understand. Yay!
- The BEST possible scenario: A complete review and revamp of all the 15 main faction regions in the game (plus tutorial zones), completely adding and rewriting dialogue and such to adapt to all the aforementioned situations. This would be a COLOSSAL work for ZOS, demanding entire regions and storylines to be rewritten considering different possibilities and such. It would be pretty much like making a new game, highly improbable that they would take this road but it would be the best possible road. Ideally, each faction would have their set of "dialogues" for quests in other faction's regions that would change all the context behind the quests but not the quests themselves. For example, saving the Skald-King could have him ask it of you as a Pact friend (if you're pact) or as a friendly foreigner (if not Pact). The quests stay the same but their stories change in a way that would make sense. This is impossible, too much work. Just pointing it out anyway.
- The most PLAUSIBLE scenario: A cautious, well crafted revamp. This would demand a lot of work from ZOS, but it is possible - to try and "draw" a single line of quests from each faction that best reflects the natural progression of that faction's storyline and enforce linearity just upon this certain line of quests. All the rest is freely accessible - other quests, delves, the regions themselves, etc. But, somehow, the "main essence" of the stories are kept together by carefully changing and adapting this one chain of quests from each faction. Also, special factional quests to "introduce" new regions/other faction's regions in a way that all the other contexts in said regions make sense. A lot of logistical work but not really much content work, this makes this way the most plausible, coherent way to do One Tamriel without ruining the game.
As always, this is just my opinion

I really love ESO, though - so I feel I must say it all regardless.

Hopefully something good can come out of it and, as usual, feel free to comment, say your opinion, agree or disagree, etc...
Thanks for the read