I think of WoW as not part of the MMO market, but the WoW market.
Plus, an MMO might do really good, and never come close tot he financial success or subscribtion numbers of WoW, and I'd still play it instead because it's not WoW. Sure, I played the game for a long ass time, but every time I go back to it or try to get into it again, I eventually run into the wall of "You must arena or raid for gear. Otherwise fuck you." Now, I don't like people much, so finding 1-4 people to play arena games with regularly is not my cup of tea. Waitingf or 24 other people to "get it right" in a damn raid instance is even less fun. So I quit, and really can't see myself going back again. If I did I'd end up at that wall again and quit.
So, a Star Wars MMO could be fun if done well. I love to harass people and piss them off though, so if there's no pvp or stealth class, I may not be interested.