I had a similiar question about insert mono/stereo handling on a support thread. In my case I have a stereo signal on the mains (inputs 1+2) and a guitar running as a mono insert on input 3. My idea was to use the INS 1 ACTIVE toggle to switch between the guitar and the stereo signal, bonus points for being able to set Insert Mix to 50% to use both simultaneously.
However, because of the mono mode switching on the adjacent algorithm, this results in the main stereo signal being summed to mono, even with the insert is inactive. (I collected some empirical data and determined that every single algorithm switches to mono except for Instant Phaser and Thru.) This is kind of unfortunate, and not at all how I expected the inserts to be mixed in.
I do like the idea of a mono/stereo indicator (perhaps on the routing view), but I would also humbly like to request more robust stereo processing. I attempted to draw how I think it should work in MS Paint (image002.png attached).