There are allready at least one similar request like this 4 years old one:
I think perhaps it's best to get many votes in one request, than have many request with few votes about basicly the same feature.
I actually don't think a feature like this should depend on a request. It's a normal basic routing in the Analog world, so it should be a normal basic routing in the digital world.
As it is, then it's possible to select a effect plugin for a instrument track. So i can't see why it should be that difficult to somehow make it possible to route audio into a instrument plugin.
Very dissapointed it's not there allready. Also for VST2 plugins and AAX that i also think support this.