pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

[Aren Siekmeier]

As others have pointed out, there isn't much reason to go with 8 motors over 6, or even 4.

But even if you insist on 8, or at least having the option to mount more motors, you can still save a considerable amount of weight and improve performance by combining 4 on a side into a single transmission, with two output shafts. You can still do so with the WCP DS components.

Duplicating the shifting mechanism on both sides adds quite a bit of weight and cost and means that shifting may not be synchronized. Separating powertrains between front and back means that you could lose half your power if you're wedged or tipped up on your back four wheels. And there's more friction and inertia with all those stages.

Also, mounting the encoder on the input cluster like you've shown will introduce quite a bit more backlash between the encoder and your wheels, and will require knowledge of the precise shift state to schedule gains properly. Combining everything into one gearbox should give you some options to keep the encoder on the gearbox if you need to, while putting it much closer to the wheel, preferably downstream from the shift mechanism.