Matt, Nice design man.
I was kinda thinking of doing something like that, except with shifting and the good 'ol 222 ball shifting.
I have some paint files of it, because I don't know how to use CAD
.
From what I can see on your design, much weight would be saved if you could make the wheel smaller, keep the innards the same but get rid of the spokes, if the wheel size is crucial in desired the desired ratio, change it some where where else. IMHO smaller is better, this is a design to save weight so try to look in all areas. In the on design I drew up, the "wheel" is nothing more than an internal gear with edges to mount brackets for mecanum rollers. Think outside of the box and go for featherweight. Good luck man.