Many people are positing that Star Wars: The Old Republic will kill World of Warcraft, that EA-Bioware expects it to kill WoW, and that it will be a complete failure if it doesn't kill WoW. Then there are people arguing the flip side, that SWTOR can't compete with WoW, that WoW will kill SWTOR, and that nothing will ever dethrone WoW.
To put it simply, I disagree with all of those positions.
The Old Republic isn't going to kill World of Warcraft, no single game ever will. World of Warcraft is too big, and too many of it's players aren't MMORPG gamers, or even gamers, but rather WoW gamers. They don't play anything other than WoW now, didn't play anything before WoW, and quite possibly won't play anything after WoW. Blizzard's behemoth is going to die though, but it will be the slow death of a thousand cuts as people leave for a multitude of reasons and recruiting replacements gets harder and harder in the face of all the other options out there. SWTOR won't kill WoW, but it will take some of the game's subscribers, and provide viable competition for future recruitment of new subscribers. Kill WoW? No. Wound it? Sure.
I don't think Bioware expects to dethrone WoW either. After all, they seem to be hoping for a million or so subscribers, which while hefty by most standards is still only a fraction of WoW's subscriber base. Anyone officially with Bioware or EA trying to claim SWTOR will kill WoW is just trying to drum up publicity. Games that seriously claim to be WoW-killers suffer some serious negative publicity when they fail. Yeah, I'm looking at you Warhammer Online. Bears bears bears. Bastards.
I think the argument that SWTOR can't exist alongside WoW is equally erroneous. If a game like WoW had existed ten years ago, then maybe I'd agree that both games couldn't survive due to WoW's enormous market share. The MMORPG gaming audience has grown dramatically in the last ten years, thanks in large part to the runaway success of WoW, and we know that the number of people currently subscribed to WoW is far far lower than the total number that have ever been subscribed to WoW. This is a huge potential market for the game (past subscribers of WoW) as SWTOR will be immediately familiar and comfortable to older WoW players, while bringing the power of the Star Wars IP to the table. It's not at all hard to imagine SWTOR bringing in a couple of million subscribers without affecting WoW's current subscriber base AT ALL. I think it will take some subscriptions away, I'm just saying it doesn't have to.
One other thing that I think many people aren't considering when it comes to SWTOR and WoW co-existing is that there's no rule that says people can only subscribe to a single game at a time. This isn't a binary situation, it's not IF SWTOR = TRUE, THEN WOW = FALSE (and vice versa). Consider that the average age of MMORPG gamers has been gradually increasing over the years. The last statistic I recall seeing placed the average age in the 30s, maybe even the 40s. You know what else increases as age increases? Income. Ten years ago most people playing MMORPGs were college students with time but no money, and maintaining a single subscription at a time was probably all most people could do. As the average age of MMORPG gamers increases, the average income of MMORPG gamers can also be expected to increase, and thus the potential to subscribe to two games at a time also increases.
The downside, of course, is that free time tends to decrease, which would be an argument against multiple subscriptions, except that games like WoW aren't exactly chock full of new content on a weekly basis. Why continue to sub to WoW for six more months until the next content patch when you could switch to SWTOR, then switch back. Not a constant multiple subscription, but over the course of a year it would amount to much the same thing. I can also easily imagine a growing number of gamers with steady incomes electing to play both games in order to maximize their gaming time. Most people I talk to who still play WoW only seriously play it a couple of days a week, and spend the rest of their gaming sessions mucking about killing time. They could very easily be playing SWTOR on those days instead.
Only time will tell, but I think the market is ripe for another big, successful MMORPG, and SWTOR isn't releasing against a whole lot of competition here. When was the last AAA MMORPG release? When is the next one? They've got a wide open window of opportunity here. I think the market is ready, it's up to Bioware to not drop the ball.