(Warning: Conjectural Forecast incoming!)
I think this could work for them. The reason Subscription models have essentially been suicide in recent years is because they're competing with WoW for that space -- but WoW is steadily losing subscribers, so that may not be an issue like it was 2 years ago.
Combine that with the fact that the F2P market is utterly saturated with subpar games(I'll grant you that has never not been the case, but remember, we're combining facts!), I think MMO players might actually be willing to pay the monthly fee to get a full package for once.
I know I am. But that depends on the game being good. That's the part we'll have to see about.