It goes without saying that ESO's base game content pales in comparison to its DLC content. Whether it's the visuals of the zones and collectables, or how those collectables are earned, ESO's base game has been left to flounder while it piles on more and more new content to just cover it up instead of elevating it, even just a little, to make it as worth playing as that new content.
From a visual standpoint even the earliest DLC zones look almost a generation ahead of their base counterparts. While ESO's landscapes can always look pretty even on low graphics settings, its old cities on the other hand are sinking in dated and not very future-proofed design. The popular cities, notably the alliance capitals all have such broad and open layouts, a philosophy stemming from the game being an MMO, thus they wanted the most populated cities to have a large layout to accommodate for the amount of players that'll be there. However as the game's grown, that design philosophy hasn't aged well, and all of these large open cities like Mournhold and Elden Root look barren and hollow, while the philosophy of newer DLC cities have realized how players move and behave, and have much more practical, visually pleasing, realistic layouts. (i.e. Leyawiin, Gonfalon Bay, Fargrave, ect.)
The rewards you get from completing content across DLC zones has (after a while of figuring it out... looking at you Gold Coast and Hew's Bane motifs...) settled into a consistent and comprehendible framework within the dailies, world events, achievements, and questing rewards, all while the base game content's rewards are stuck in the mud of either being nonexistent, inconsistent with how other rewards are distributed, or just not up to par with what new content has to offer. (quests just giving you named leveled gear that's not even part of a set, a whole polymorph from a random quest in Shadowfen...)
Slightly walking back into graphical discussion, and maybe one beyond the scope of a discussion of a base game overhaul, but one of ESO's weak points is its player model. I've never really had a problem with it, and always thought people gave the game's models too much grief in the earlier days, but recently when making some new characters and playing through some old zones, some things really started to itch me. It can likely be attributed to the model's low poly-count, in combination with how limited the sliders are, that it seems no matter how you make your character some things are always constant. Females will always have noodle-y arms and cinched waists, males will always have triangular or rectangular torsos and flat... posterior dimensions... Perhaps most damning is how limited the facial sliders are. It feels like the only slider that really changes anything is the overall-shape triangle-slider at the very top, after that everything else just changes the face by a matter of millimeters. Taking all that into account, it feels like this produces the symptom of so many player characters and NPCs having very same-y appearances outside of outfits or sparkly cosmetics. Indeed it feels like ZOS intended to paint over their shoddy work on the body models by just making more and more detailed motifs and costumes to accompany their new content, but that in-turn created another disparity... Old cosmetics look terrible now in comparison.
Probably the most controversial notion I have to propose is that the base-game motifs, from the 10 racial styles all the way to Daedric, Dwemer, and Akaviri, also need to be touched up. Now, I know the Ancient/Ancestral motif variations exist to solve this issue, however they're a bandage solution. They're just higher quality reimaginations of the old motifs, but the old motifs still exist... and they're a little rough. I don't think they need to be updated to the level of detail of their newer counterparts, but they just need a bit of a boost in their texture resolution and polycounts because as it stands, the base game motifs are basically impossible to use alongside anything except themselves without the outfit becoming as ugly as an Ogrim.
A hypothetical base-game overhaul update like this would also be a golden opportunity to possibly introduce some of the more important systems added in the chapters into the base-game. (assuming a given chapter hasn't already been made free to all players by the time an update like this comes around...) There could be Antiquarian enclaves added to the (newly remodeled) alliance capitals, and there's already jewelry crafting stations at most crafting hubs, so jewelry crafting could be made base-game as well. Of course, this notion of giving away once-payed content for free seems repellant to the Zenimax we know, so let's put this in the "optional" column.
Without elegance or grace, I'll segue to the short and simple point that such a base-game update could also introduce some of the overland improvements/difficulty we've been asking for, and have seen some of in the newest content, into the original game for players new and old to appreciate.
I would've ended this with a mention on how a base-game overhaul update could also introduce changes to questline progression and putting in some safety nets to keep players from sequence-breaking themselves on accident, but I remembered I wrote a whole other essay on that in my past post about the "New Player Experience" and to do so now would be redundant and... exhausting.
*empty*