“You would have to build something very console centric from the get-go,” Paul Barnett (WarHammer Online Creative Director) said in an interview with ComputerAndVideoGames.com, “I think probably the best chance of someone doing something like that is Nintendo — doing something crazy that no one expects.”

He also suggests that the key difficulty for crafting an MMO for consoles is the mass fondness of World Of Warcraft.

[Rob's Opinion] I feel that he is simply bringing up WoW because he is developing an MMO that directly compeats with it, that being WarHammer Online.  I have my doubts that WoW hurts any market of games other than the MMO market.  If anything, WoW has helped the video game market by bringing in new players that have never been into video games before.

This also holds true for the Nintendo Wii, as that system has also brought in new gamers.  While I personally would not buy an Animal Crossing MMO, a Pokemon MMO is not out of the question