Postulating that Tabula Rasa will open the door for new game models to sneak into the MMO genre, Keen wrote: "A storm is brewing and the winds of change are going to be mighty strong."
If there's a storm brewing, I expect a light drizzle. No thunder, no lightning; nothing to catch the attention of the folks inside (the people who aren't already playing MMOs).
It looks to me that The Agency will be a bigger step away from the traditional MMO model than Tabula Rasa is; and it's significant that The Agency is by one of the main players in the genre, SOE. Still, I doubt even that game will be successful enough to take everyone's eyes off WoW. Developers will go on mistaking World of Warcraft as the pinnacle of MMO gameplay for years to come (I am thankful to Richard Garriott, though, for publicly stressing that they're mistaken). And when WoW is a distant memory, the mechanics which drive it will still be around.
The MMO genre won't experience any sweeping changes soon or, perhaps, ever. What will happen is we'll see more games blurring the boundary between MMO and other genres, like Hellgate: London and Habbo have done.
Hellgate is focused far more on small groups and individual players than on a massive community... which is why a single-player, offline mode is even possible. Habbo, on the other hand, is a social sandbox in which most goals are invented by the players, rather than the developers. In the nature of its appeal, it's more similar to Myspace than to Everquest 2. Yet both Hellgate and Habbo are regularly referred to as MMOs.
One by one, developers are going to design games with oddities like these; oddities which are noted but have no widespread impact on the genre. One by one, they'll sneak in there... until one day we all look around and say, "How did we get here?". The genre's eventually going to look different, alright. But the change is going to come so gradually that most of us won't even notice until it's already happened.
I forget who said it, but some developer once pointed out that "Massively Multiplayer Online" is not a genre of games in the same way that "First-Person Shooter" or "Real-Time Strategy" are. "FPS" and "RTS" summarize styles of gameplay in ways "MMO" doesn't. If a game isn't in first-person perspective or doesn't focus on (or, at least, heavily involve) combat, then it's not an FPS. But just look at the differences between all the games popularly called MMOs!
Perhaps, ultimately, that's the reason change will come gradually to this genre. One FPS game can change the whole FPS genre because most FPS developers are focused on the same goals and most of the genre's games share one audience. Different MMOs, on the other hand, focus on different elements of gameplay (such as RvR, small group instances, solo play, etc) and there's less crossover between players of games.