The big issue with making a MMO that works for a console is the limiting controller. The typical MMO requires lots of button combinations and often multiple button presses at the same time, additionally targeting and camera rotation is usually achieved with the mouse.
Blizzard have said they are having talks with Microsoft about developing a controller that would tackle these issues and make it easier to play MMOs on consoles. This would be a big plus for both companies, for Blizzard they would be able to reach additional customers, and for Microsoft more games would be made available for the xbox. The obvious solution is just to plug a keyboard and mouse into the computer, however I doubt that is what they are going to come up with, expect something new possibly including motion detection similar to the Wii controller.
It is possible that the console controller could be released alongside Blizzards new MMO, although this is pure speculation.