There are a couple of undocumented shortcut keys already.
Function Key
--------- --------
Cut 0
Fade 1
Fade 2
Fade 3
Fade 4
Fade 5
Fade 6
Change Preview Input q,w,e,r,t,y,u,i,o,p (in order as the inputs appear in vMIx, for example R would change to the 3rd one across)
Also, a mute all button is easy enough to implement, I may just enable an option in settings to mute all inputs by default then you can select what to enable as you need to.