I spent enough years of my life repairing electrical appliances. One truth is that the more complex they are, the more that can fail. Guitar amps are fragile enough as they are. For that reason, I say:
If you want to develop midi switching, make it in a separate module. Integrating it into the amp means that when something goes wrong, you lose the whole amp. Making it modular means if anything goes wrong, we can replace one simple module, or in case of emergency we can fall back to the footswitch tap-dance and get through the gig.