The Daily Grind: What genres will never work as an MMO?

Lately we've begun to see the shooter genre creep into the massively multiplayer online game space. Titles like Global Agenda and All Points Bulletin are both equal parts shooter and MMO. Assuming the trend continues, we'll probably see more shooter MMOs in the coming years -- potentially even other genres, too.

Obviously, this makes most of us wonder what other genres could hit the MMO scene. But, what we really want to know is which combinations you think are lost causes. Will there ever be a successful MMORTS? If not, why? Would anyone even want to play an MMO version of a fighting or racing game? The mind reels at the possibilities.