The days of subscription based MMOs are definitely over. There's Tera which I heard is doing alright, and obviously there's WoW and EVE, but other than that I can't imagine any subscription based MMO to be successful these days.
Final Fantasy XI is still doing fairly well, but it'll be interesting to see how Final Fantasy XIV and Dragon Quest X do. The latter will probably be fine in Japan and will also have free play periods daily (intended for kids who can't afford an MMO, but it doesn't verify age), but the Dragon Quest brand isn't nearly as strong in other regions.
And, of course, XIV is another story entirely, especially since they've spent all of that money essentially devloping the game a second time. I wouldn't be surprised if they've already got a free to play structure outlined just in case.