I've got a rough idea of how this could work:

XLR in would feed into some kind of backplane with slots for inserts to be added.

A master Arduino would read button presses from the box (currently thinking of a long H hammond style enclosure at the minute, or a custom wedge shaped box) which would then control which insert points affect the signal, before heading to the XLR output. Id like to have a dry output as well, for options.

The inserts would either be Pi Zero boards or Arduino boards pre-coded to carry out a particular signal processing task.

I'd also like to have one of the inserts for a volume pedal, and one or two jack sockets for expression pedals to be added. These could be read like potentiometers by the inserts.

There could be a lot more efficient ways of doing this, such as true bypass switches, but the thought process is a fresh one ha ha.