In MB you have the option to assign "free" sidechain areas for each individual band, this is really great. But what I'd like to see is a option to increase the gain of these SC areas, so that certain individual band is more sensitive to SC area, less sensitive to other area. Maybe while we are at it, you could add 1-2 new SC areas for each band?
One usecase for this sort of "complex" sidechaining is when you have a microphone with no shock mount, and so the microphone is sensitive to table vibrations, but possibly also to keyboard clicking.
You can downward expand certain frequencies to avoid table vibrations with a mic with no shock mount, you set lower frequencies on "gate" mode, with SC frequencies around 700-1000hz. This is easy to do, but it gets tricky if you want to simultaneously gate both "keyboard" clicking, and the table. It can be done with multiple instances, but maybe with more complex side-chain options (each band could have multiple SC areas, with adjustable gain), it could be possible to set-up so that both the table vibrations and the keyboard clicking, could be fixed in a single instance of MB.
Did I mention this is ideally for real-time? For normal DAW use it's no biggie to have extra instances of MB open, but since MB is no ZL, it'd be great to be able to do this stuff in a single MB instance :D