I can't say for certain that the free-to-play business model is going to replace the subscription model in the MMO industry in the future, but I can say that games who have recently made the switch are seeing positive results.
Most recently SOE president John Smedley revealed the user statistics for Everquest II since its switch to free-to-play, and the numbers are quite impressive.
Announcing the numbers via Twitter, Smedley revealed that EQII has seen a 40% increase in daily logins since going f2p and a 300% increase in new players.
In addition to the growing number of players, they've also seen a 200% increase in in-game item sales.
"We have added a lot of new subs," Smedley said. "all during the time that some really good competition hit the market."
It's quite impressive that Everquest II has managed to increase its player base, especially given the launch of the highly anticipated Star Wars: The Old Republic.