That solution already has that switch: it's one of the strong points of that build, imo. Unfortunately, that solution also does away with the raspi ports, which I think is a bit of a shame. But if a case builder could help out with this and design the case to accommodate the port holes in the back of the keyboard case and leverage the keyboard's back slopping, this would be a cool new option, that wouldn't sacrifice the hardware.
Maybe someone with case building experience could give us an opinion?
About the PI model choice, my opinion is that using a raspi zero, is an insufficient performance solution for some software. Heck, maybe we could have case slots for both models.