[Geoff Waddington]

FYI update.

Have thought through the "engine" part of this and am about to start coding said engine.

Basics are this:

External control surface can send message to Reaper.
Reaper can execute ordered list of things when it receives message.
Reaper can send feedback to external control surface(s) in response.
Reaper can send message to control surface(s) whenever a certain event happens in Reaper.

There is an incredible amount of detail missing but that's the basics.