They're all possible. Whether or not they're likely is a different question...

MS Word: we've got Abiword already.
Citrix: no chance without Citrix's involvement.
Push email: there's Telomer already, but anything else I'd be surprised by.

Not enough tablets have been sold to make any commercial investment worthwhile, so the best chances are existing open source projects ported, or new ones started from scratch. All of these are in people's spare time, however, and I've *personally* got the feeling that now the hype has died down, the number of people able to do truly cool things with the tablets are few.

Hopefully the efforts to get Java running will ignite some more re-excitement, and not just result in Yet Another Media Player front-end.