Blizzard's Tom Chilton on the future of WoW on VideoGamer.com discusses the future of World of Warcraft (thanks Joystiq). They ask about the business model for Blizzard's MMORPG, and Tom does not rule out the possibility that the game could eventually evolve to use a subscription-free model with microtransaction support, though this would be way down the road:

I certainly think it's possible that we could do some kind of micro-transaction stuff. Whether or not World of Warcraft ever goes the direction of, I guess like Anarchy Online has gone the direction of going free-to-play with micro-transactions. Whether we ever shift to a free-to-play model is really too hard to say at this point. Anything I say now could easily five years from now end up seeming like, oh my gosh, that was an incredibly dumb thing to say, how naive!