Assuming the hypothetical scenario of this game actually coming out the way the people are hoping for; even though that seems to be a faint dream; I will vote yes. However, there are many things we have to look at here first.
Take for instance the beginning of Fallout 3; where you are born, and then there's the story that continues on with your father. Obviously, if they made an online Fallout this could not be the case. You most would have to choose a past for yourself so 1,000,000 other people don't have the same past as you; that might seem a bit odd.
Apart from them needing to be careful on what they make the plotline as well as your character's history, they will also need to think about guilds/groups. An MMO is never really a true MMO without them. Either that or it's just not a good one. I've also read another post speaking of a karma pool, in which one person's moral desicions affect how others treat people that person works with, which can tie into guilds/groups thought. I do not want to say how they should make the game, I only want to say what they're going to have to think about. What will be the code of conduct, how will moderators...well....moderate the game. Will they allow others to loot from bodies of people that they didn't kill, and if the loot from, let's say a cabinet, will the contents be gone for a time for everyone, or will the contents only be gone for the person who took it. You cannot simply say "We're going to make an MMO based off of this" and then go with it. An MMO is without doubt one of the hardest if not the hardest type of games to make. What I would suggest to them is to create what they can now, release it only to a certain community, get opinions, expand, upgrade, and build up to the time when they truly think that it's ready for the public. If they have any financial trouble whatsoever, I then suggest that they don't even try with this, because if you try to just squeeze by on an MMO with even the slightest budget problem, the game will end up being useless crap, and you won't make any net income anyway and you'll just be wasting whatever money you have left.
I would like to apologize to anyone who may think I'm addressing them in an ill manner, but I am only stating what I think about this entire idea.