FFVIX is about as important as Aion, Warhammer Online and Star Trek: Online. In other words, its just another in a long line of similar MMORPGs made to just try to take its own small piece of the overcrowded MMO pie for a time until it stops making money.
Based on the Final Fantasy name, hte previous titles established core fanbase and the high graphical output of the game, it'll probably last longer than most MMOs. However, will it 'impact' the market? Not really. If anything, it'll be labeled as just another peg on the WoW ladder.
The only MMO that really looks like it'll have any chance to go up against WoW anytime soon is Star Wars: The Old Republic. And in Asia, POSSIBLY the Dragon Ball MMO, but they have been working on that for almost 6 years and still aren't releasing it, so it might as well be the 'Duke Nukem Forever' of the MMO world.
Six upcoming games you should look into:
