Honestly, it's a dream, but I'd love to see the term "casual" disappear from the MMO community lexicon
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It is now so heavily loaded with negative connotations as to make any sort of objective discussion difficult.

Unfortunately, the lack of a suitable alternative term means this is unlikely to happen any time soon.

The only thing that matters is if you're enjoying the time you spend playing ESO, no matter how you choose to spend that time.

That being said, every successful game should always have some thing that some players are not able to accomplish without a certain investment of time, skill, or both. If everyone could do everything in the game with no requirement of skill and a minimal time investment, not only would the game become extremely boring very quickly, there'd be no motivation to ever improve your gameplay.

Pick a sport -- any sport -- let's say golf in this case
Even the best golf players in the world cannot beat par on every hole on every golf course every time.
There have to be elements of risk (sand traps, water hazards, terrain features), skill at play (distance, direction), and physical skill (swing mechanics, foot and leg positioning, physical strength and endurance) in order for the game to be enjoyable and fun. There also have to be elements of reward (pride, competition, ranking, trophies, prizes, money, a feeling of accomplishment) to motivate players to complete the golf course as best as possible, and to motivate them to improve themselves so that they reduce risk and gain reward.

If someone who's never picked up a golf club in their life and someone who's been a consummate professional for 30 years could both perform nearly equally on the same golf course, for the same given time investment, both players would burn out very quickly and have little motivation to keep playing in the future. This applies whether the game is way too easy, way too hard, or even just moderate difficulty. It's not the difficulty of the game that's important -- it's that difference in players, from one extreme to the other and everything in between, that makes the game rewarding and enjoyable and motivates participation.

Skill = ability to play a game of golf at a given level to earn rewards (tangible or psychological or otherwise), whether that's the newest player or the most experienced.

Accessibility = being able to get on the golf course to begin with, and providing things such as training, equipment, repetition, practice, and education in order to improve one's skill.

Me and three friends might not ever be able to even hit par on the local course, and we score 20 or 30 above par, but we have a great time when we play, because of companionship, regardless of skill. The ability to get better is always there, if any of us want to take it -- and that is accessibility. We could take golf lessons, work on our swing mechanics, read books, watch videos, or practice a lot more at the driving range or by playing a lot more golf games. The accessibility is there to let us grow our skill, if we decide that would be more rewarding.

I would therefore consider us "casual" golfers in a positive sense. We enjoy playing the game, we are able to play the game at a level that we find suitably rewarding, and we have the opportunity to improve our skill if so desired. Our livelihood and paychecks do not depend on our ability to play golf (thank goodness.) We don't spend most of our time playing golf, or devote a lot of financial or personal resources to the game.

To reframe that conversation in terms of ESO:

Skill - the ability to complete a quest, a dungeon, a trial, a PvP objective, a crafting task, an endeavor, or an RP/social engagement at a level that makes you feel as though you have accomplished something / been rewarded

Accessibility - providing players who want to do those things the tools / means needed to obtain a level of skill sufficient to complete their objective, whether that's guildmates, friends, online guides, videos, in-game tutorials, learning by trial and error, or just jumping in and giving things your best effort.

Accessibility is something that should be a given. Skill is not. It's okay not to be able to do every possible thing in ESO. The problem comes when people get out of that mentality and start expecting developers to change the game to match their skill level, instead of increasing their skill level to match the difficulty of the content. At that point, the game becomes less rewarding for everyone.

Casual player - plays ESO in a manner which they find rewarding; has the means (accessibility) to improve their game play to earn better rewards or more personal satisfaction if so desired; does not feel obligated to play the game any more or less than they already do, but can do so if they choose. Does not schedule all of their real life events around ESO events, but could if they wanted. Is not financially dependent on playing ESO as a means of income or survival. Can play ESO for 8 hours a day, or 30 minutes a week, and be equally satisfied.

I consider myself a casual player.
And while people are right in saying there are a lot of different definitions for that term, I found my own one.

I've been playing ESO since 2016, usually several hours on several days a week. It took me a few weeks to get a grip on how fighting in the game works, because the only other "real time" (not turn based) things I had ever played were TES III - V, and I was slightly overwhelmed and hectic at the beginning, having to move my character, watch the environment, and press skill buttons at the same time. ;-)

Ever since then I was able to play this game the way I'm used to, no matter what changes to abilities, equipment, sets or other combat stuff were implemented. Because for the things I do and the way I do them those changes have never made a relevant difference.

[The one thing that actually changed anything for me were companions. Basti made things on the edges of my ability a lot more comfortable/possible. Like soloing dolmens, geysirs, public dungeons or non-DLC world bosses. And I love having him around.]

I do everything the game has to offer except these: Trials. Battlegrounds. Vet Dungeons. Hardmodes. Dark Brotherhood stuff.
No Arenas beyond Maelstrom Normal/Dragonstar Normal with friends (and both of these only super rarely, when events make it necessary).
PvP I only ever do by joining large groups, usually during PvP events, usually for a few hours at once, for one or two days per event, for the fun of seeing the AP and/or the loot rattle in, not for fun in actually fighting other players. (I do my part to support the group with siege, skills and following orders, though.)
Normal Dungeons I only do with premade groups, once to see the story/get the skill point, afterwards usually only during events that reward them specially, or to help others who need a tank/group member.

I am in a very casual social and in a trading guild. I never took up any obligations to do specific things at specific times, or even at specific requests, I do things when I want for as long as I want. Usually solo, sometimes with friends (dungeons), now and then with random groups (world bosses or randomly helping out others with whatever).

So for me, the "casual" has two aspects: I'm independent from combat system tweaks of any kind (because I do no "hard" or competitive content), and I'm free in using my time in game.

That said, I'm afraid that whatever ZOS tweaks on the number front probably won't make the hard or competitive content a lot more "accessible" to me.
To do that they'd have to dial back on the stuff they love so much in their new dungeons: Combat-in-full-movement. It's not the numbers, it's the multitasking. I'm plain unable to cope with moving my character around while at the same time moving the camera around (or at least my attention) while at the same time using and aiming skills.
And every new dungeon seems to have more and more and more "everything willl be red, you have to constantly move, while watching several sources for several tells, while aiming at several things, and having to get to very specific locations while doing all that" sequences. I tried avoiding the brunt of that by playing the tank, but it is just unavoidable in vet.
And PvP in the literal sense (facing off against another player via our characters) just holds zero interest for me.

@JKorr @barney2525 You both summed it up quite nicely and spared me having to explain, yet again, why I couldn't be paid to do pvp.

To those wondering how I can detest something I've never done... see Jkorr's post and one of my roommates does pvp sometimes and I've spectated in the past... yeah, never gonna do that.

My two cents:

I think the words Casual Player and Accessibility are just brands at this point and are being (mis-)used to compartmentalise the community into smaller groups, that are easier to handle.

ESO offers such a broad variety of playstyles, difficulties, lore and content, that it attracts an equally broad variety of players.

"Play how you like" also means: Let others play how they like!

A little more respect for other players and their ways would bring the entire community a long way.

I believe that „casual“ basically means playing at their own pace, not jumping on every hype/meta train. Forming the game according to that means that you have to be able to afford missing out on things and yet not be cut off from the general evolution of the game, to be able to catch up with the others. This is the main challenge to keep the business of a MMOG growing.

I have been playing and subscribing since early beta, but I am still at around only cp 1300 (had to switch mega servers in between, but that is still low, considering the years).

I have been on and off, going in at times for certain “projects”, like building that one meta sorcerer, getting a certain set, or house, achievement from a trial etc.

This way, I have done almost everything at least once with one of my characters. But I still suck at pvp, have trouble weaving properly and have family and a demanding job etc.

That is casual, imho, and I can still “access” almost all content in my own time, which is the accessibility, ZOS is cracking their heads about.