Seems like an easy mod in concept but if the circuit boards are mounted such that you'd have to cut them up then I can see why it's not a popular mod.
Also, I don't know this amp but if you think about using the amp as a two-channel amp then you need separate Gain controls and separate Master volumes for it to really work right. Don't know if it already has those or not but in any case, that's more relays/optos/complexity.