For a (non-FPS) PS3 MMO to work out you would have to revolutionize the UI to work with the limited console controllers.

Personally I think I would build the game from there. Use the standard MMO model as a reference and see how a simplified interface changes the focus of the game. Iterate on that until you have something thats fun to play.

If SOE publishes an MMO specifically for the PS3, I wouldn't expect any great innovations in the gameplay model itself. They'd want to reduce risk as much as possible by using a proven model. Achievements, built-in-Voip, tie-ins to Home, sure but nothing in the core game itself.