I would highly suggest against pocketing your motor mounting plate like that. Not for strength concerns, but for cost and time. The weight savings simply aren't worth the headache.

That being said, Nice design! Ought to make everything nice and integrated. If you can figure out a system to make each side of the drive system modular (IE GRT in 2007), it would add to the system's robustness and quick-changeability during competition.

I'm still waiting for a team that can pull of Nascar speed pit stops for battery and drive changes. It'll be cool to see a team rush into the put, drop the entire robot base (drive+battery), latch a new one on, and rush off. You know, I think my CAD setup is calling me...