Not only do I like this idea, I would expect it to work on a scene by scene basis. I'm currently simulating this through my Behringer XR 18 mixer/interface so that I can route a Guitar Rig 5 instrument and my microphone to separate inputs on an audio input channel to turn TAL-Vocoder 2 into a virtual talkbox. It would be fantastic to do this natively inside of Forte instead of having to route it back through my mixer. It would also require being able to pan to left or right on the instrument in order to support this specific scenario as one channel is carrier and the other is modulator for the vocoder.
This would include an Aux fader or pot in each instrument channel and bus, right? I heard from many potential users that they were missing this.
It seems that this is a functionality implemented in just about any other host I know of, plus, if Aux Bus does not work reliably in all circumstances, there is no workaround.