We did something very similar to this for our drive this year, and it saves about 1.5" on each side, which we needed for our shooter. This looks like it could be useful
It’s hard to see in the picture, but the shaft that we use to shift is the one in the middle (with the 56 tooth lightened gear), and the pneumatic cylinder is on the other side.
The only issue with this design is that the final reduction stage for our high gear needs unusual gears because of the additional torque from adding a third CIM. Most 20 DP gears used in FRC gearboxes are 14.5 degree pressure angle and .375 thick, but we needed to use steel 20 degree pressure angle .500 thick gears to prevent shock loading from snapping off teeth on the final 18 tooth gear. Surprisingly, we’ve had no issues with the cantilevered gears, except for cables getting stuck in them.
We also found it really helpful to have our center wheel’s shaft be 3/8" steel hex (we did support this slightly smaller than usual shaft on both sides of the wheel) then weld a hex sleeve onto our output shaft so our gearbox can just slide in and out of the robot. We only have to undo two bolts to pull our gearbox out.