Allowing individual subtrims for each servo per flight mode.
I would propose one general subtrim per servo. Plus optionally a delta on that for each flight mode.
Bertrand has worked on something that looks similar, but he used GVAR. I think it should allow GVAR and manual values.
This feature is especially useful for gliders with multiple servos per wing.
It can be practically impossible to drop all servos down or up in a straight line for camber control. (different non linear linkage geometry and different servos)
This way one could create for example a slow flight flight mode with a few mm camber where all surfaces move the neutral position down to one straight line.