Outrunners supported/held by the shaft?

[sikeston34m]

This is do-able for sure as long as you consider gear ratios and roll out in your setup.

By connecting the endbell to the diff, you're adding a flex point.

You can get by with this, as long as you use a motor with the endbell bearing. It's a press fit, but will prevent the magnets from contacting the stator during hard acceleration or braking.

Does your motor have the larger press fit endbell bearing?