maybe I’m just still not really understanding MIDI, but what if the sampler instruments in renoise where configurable in a way to listen to certain MIDI ‘channels’ - so you can easily in that way map (through pd optionally, or another program, I don’t know) different parts of the same keyboard/padcontroller to different instruments? (mainly because multi sample instruments in renoise still suck if trying to use it for drumkits. always some stuff you end up being unable to do, like pitch up/down individual hits)
The MIDI Input section already lets you choose MIDI Device and MIDI Channel. If you can split your keyboard over multiple channels you can already play more than one instrument at a time with it, and even have them assigned to their own track.