[asid61]

Looks interesting. The lightening pattern and flanges on the caster box look quite strong. You may want to model the tread on the wheel to be sure it fits. A nice set of speeds, although a tad fast for the high gear. I bet you could swap a CIM pinion and fix that, but it's no biggie.
Is it possible to turn it into a 2-plate design rather than a 3-plate one? This would reduce size and weight. Is it possible to flip the CIM? That lowers center of mass quite a bit.
As it stands, you could probably move the turning gearbox one plate lower. The extra mounting points for the motors can be removed via Configurations, so I would use those and cull some weight that way too.
What is the weight?
Where are the encoders?