Going to make a couple comments here. Some are, or seem like they should be, obvious.
-MMOs are a completely different genre of game. One might effectively argue that the typical MMO and the typical Beth game are diametrically opposed in design philosophy. There is an excellent opinion piece on Gameinformer outlining this.
This is fundamentally wrong, and I read the incredibly uninformed GI article as well which was nothing more than a fluff piece coming to the defense of the game they were featuring at the time. MMO stands for "Massively Multiplayer Online." That's the only requirement. A large number of people playing in the same virtual world. MMOs actually span several other genres and are not a genre unto themselves, they are simply indicative of a mechanic. MMOs can be RPGs, Shooters, RTSs, Space Sims, etc. MMO is only a qualifier that states that this game has a lot of people playing it together. If you go into a pitch meeting and say "I want to make an MMO" the first question you will be asked is "what genre of MMO?" Trust me, I've been there.
When you attach the word "typical" to it, then the argument changes to this: why bother making a typical MMO then for an atypical RPG franchise? As I already stated, there are already several MMORPGs that have proven that many of the mechanics and design philosophies used it TES games would work in an MMO environment, with only the most minor or inscrutable tweaking. MMOs are huge investments and undertakings, and if you can't stand out, you perish.
-Using the TES IP for an MMO, because of the above point, is rather interesting, because TES fans who have never played an MMO will probably hate TESO, because by it's very nature as an MMO, it will not be able to deliver the exploration, the worldchanging Hero quest or the extensive world interaction that a single player game may provide. MMO vets won't care as much about the IP as they will about the mechanics; specifically in terms of combat, PvP and end game progressions. There isn't much built in overlap here, and because of that, TESO systems and mechanics will be geared toward MMO players (It's an MMO, after all) and not the desires of TES fans. And of course it's about the money: They are in the business to build the best game within budget in effort to provide the best shareholder value. That's what "business" means.
Being a part of the business you speak of, I have quite a bit of experience here. The problem is that they are not pushing away TES fans on purpose. There are plenty of TES fans who also play MMOs and enjoy them (I'm one of them) so there is definitely market overlap. The problem, as you already stated, is that Lore is by and large not as important to the TES IP as the mechanics are. At the very least, the mechanics are what set it apart from other AAA RPG titles. TES almost has a monopoly on immersive, open-world action-combat.
Knowing how the bean-counters tend to think, the same conversation is going on in their meetings as were going on with TOR and LOTRO: "We have a built-in fan-base! We can quantifiably rely on [this many] people to buy/play this game, then we branch out from there." That quantifiable fan-base is the TES fan-base, not the MMO fan-base. The MMO fan-base is an unreliable number and tends to be nomadic in nature. As we've already established, by and large the TES fan-base are in it for the mechanics.
They are using the mechanics to try and grab as many of those non-TES fan MMO players as possible and what they aren't realizing is that that was what the MMO audience might have wanted in 2007, but no longer is it what they want in 2012. Will they settle for the tired old, stale systems they are used to? Sure, but will they love it and stick around? No, not unless it brings something fresh and unique to the MMO table. Skyrim-esque combat is the NO-BRAINER mechanic that will do that. Is it actually fresh and new, no, other MMORPGs have had Skyrim-esque combat, but they have been tiny niche MMOs with less than 20-person dev teams, no funding and absolutely zero brand recognition. They've already done the experimenting for ZOS. If ZOS would realize any of this then maybe they'd have a shot in hell of achieving the success that I'm sure their shareholders are predicting with their "we can't lose" attitude.
Fundamentally, if it's going to play like WoW or Guild Wars, the MMO players will already have those established worlds with their guilds to go back to. Remember, MMOs aren't about sales, they are all about retention rate.
-TES fans won't care one bit if TESO fails, as long as the next TES game is released. Success of TESO might drive TES sales to some degree, but the failure of TESO will not necessarily damage the TES franchise. Games like Skyrim and the Fallouts are so rare there there is effectively no competition, and even if there were, the sandbox RPG market is about as far from saturated as one can imagine.
True, externally, but internally you can't be so sure. Shareholders aren't going to differentiate between TESO and TES VI. It's another AAA big-budget game in the franchise to them, that's it. The fact that it's an MMO or a Single-Player is splitting hairs to them. Even being a different development studio, it is still overseen by Bethesda Softworks, the publisher, which is just one rung under Zenimax Media (where all the money comes from). If TESO fails, dies or goes free-to-play within the first year, that will reflect badly on TES as a whole in the eyes of the shareholders and executives. Your IP is only as good as your last product. TES has been batting a thousand, growing exponentially with each iteration. You better believe they will be expecting the same growth margins from TESO and if it doesn't hit them, it will be very hard to justify pumping as much money into TES VI as they did into TES V or worse yet, allocate all of BGS' resources to the Fallout franchise for the foreseeable future (they're already working on Fallout 4 as we speak). On the other hand, if it succeeds, ie: makes its budget back plus 25% in the first year of release (minimum success ratio), ZMM might demand that TES VI take on some of the mechanics of TESO and it will be a tough fight for BGS to keep that from happening.
Hope for the best, but prepare for the worst. I sincerely hope it has no bearing on the TES franchise as a whole, but I'm not naive enough or inexperienced enough to believe it won't.
Also, speaking on a personal level, I have always wanted a TES MMO in a way that would bring TES into an MMO setting. Knowing it is perfectly possible, I am saddened that they are not taking steps to do that. So don't assume that no TES fans care, because my existence proves that point moot.