The thought of having Fooruman at all is leaving a very bad taste in my mouth.
Last I checked the working title is "Jazz RPG" not "OMG CROZZOVAR
STARING JAZZZZ JACK RABIT!!!111!".

Plus if History has taught us anything its:
The only crossover games that are good don't have much of a storyline(well not much ingame anyhow) or, are TCG games(ala Card fighters clash).
The only RPGs that are good(using the standard Casual Gamer, and magazine standards) have alot of storyline.
Theres a big conflict there.

If anything, make a new villain instead of shoving the same tired Turtle and Wizard down our throats.