As you state a multichannel mode would basically require hardcoding some default MIDI channel number choices like using 1-4.
Things could be made more configurable by leveraging teletype - but that requires a second piece of hardware to configure features which in my opinion is not great from a design standpoint and bad from a karma standpoint. That said there are a few features of the midi arp mode that are only accessible via ii commands…
I do see some value in a 4 channel mode with pitch and gate out and well as a 2 channel mode with gate, pitch, some cc, and a note off trigger.
The front panel buttons are already heavily overloaded with combos. IIRC the logic to save midi mode configuration is a button combo that flashes the mode light to provide feedback.