I would love the ability to output any mixer channel to any output, but with a choice between pre- or post-inserts.
A typical use case would be: you may have all your mixer channels routed into your Master bus, and your may have some mix bus FX in there, which is a typical scenario. But then, you may want to add a 'Reference' channel where you drop some reference tracks to compare your mix with, and you obviously don't want to have the Mix bus FX affect this channel.
I know I could simply create a separate virtual output routed to the same physical output of my interface as the Master bus, but here's the catch: I may be using some metering and room/headphone correction plugins as a post-insert on my Master bus, and I will obviously need to have these also on the Reference track's output to get an accurate comparison, which forces me to duplicate those plugins and also to change settings on both every time I want to switch between let's say room speakers and headphones monitoring.
This is only a very specific case and example but I envision that this feature would more generally be a handy one in other situations too, even with creative mixing and routing of tracks and effects to Master buses.