Modeling (particularly with the pure poly world you’re talking about) can be done in any app, however the rigging through render part of the pipeline really needs to be kept in the same boat.
Yeah, it’s possible to use motionbuilder as an intermediary – but that’s another piece of software that people will need to have in order to contribute. As such, I think it’s a bad idea. I think you’ll find that the majority of pro level rigging talent on here is maya-centric, although I might be off-base.
I say pure poly world, but a fair amount of the squash and stretch effects I saw in the storyboards look like they would benefit from sub-d or nurbs workflow.
If we were talking about a more taxing render, the app in question would really be driven by what renderer we could get on a ton of volunteer farm machines. Luckily, I don’t see the finals taking more than a few days on a few machines – even if we were to go all out on multiple passes for the benefit of the post artist, or to even render in HD. In my wildest GI/FG/DOF/Motion Blur dreams, I can’t fathom more than 20 minutes a frame at 1920 rez because of the simple texturing.
I’ve got an interest in using Maya from a purely selfish standpoint as a potential lighter. I also think the flexibility in renderer choice (mental ray, turtle, renderman) would be a bonus, although the same argument could be made for 3ds.
As a potential editor/postmonkey, whatever app delivers me clean render passes as 16 bit per channel TIFFs (monochrome world will benefit from the added data in post) that I can massage in After Effects and/or Final Cut Pro (could also use my office’s shake license, for the record) gets my vote.

If that’s not going to work out let me know.
