i don't think it's going to be a new tablet - i'm betting on the "two box" theory. A small "box" that will take care of translation between WiFi/bluetooth to the WiMax network. This "box" will also provide the subscriber authentication means (sim or whatever it is).
would be easy/inexpensive, and in my view the most important, enables WiMax for all tablets. (sarcasm: no-it's not a phone! )

<NOMEX flame suit ON!>

-Matt