Why then use instrument tracks in the first place? Some people actually use them. And there is no use in hiding, because those people need access to both parts of them (audio AND midi), but if they are in the same place (combined in one track) access is easier and slimmer.
So instrument tracks are a used feature - why not make them usable with multitimbral synths?
I don't know, how others work, but I have, let's say, 10 Instruments. If you have all of them in one Kontakt instance or let's say in a Vienna Ensemble Pro instance, you can't use Sonar's instrument tracks.
So each instrument has 2 tracks, which are named "Piano MIDI" and "Piano AUDIO" ... 20 Tracks. If you work with the VS-700c console ... well space is heavily wasted and you keep switching banks. No sense in hiding, because you need MIDI and AUDIO. Sometimes you hit the wrong track (MIDI instead of AUDIO) ...
All of that could be really simple with multitimbral-ready instrument tracks.