The other really useful thing for plugins inserted on cue or device outputs would be the ability to send MIDI program changes, and cc data, to them. This would increase their usefulness exponentially. At the moment if you want 10 different reverbs at different points in your show (and the plugin you want to use wont work as a cue effect) you need to have 10 reverb effects runnimg continuosly on different busses, which is a significant hit on performance.
If you could send MIDI to the plugins you would only need one instance running.
Mic