Oh yeah... for me and you, this is not really necessary.
But still, it would be cool.
Are there no Cake FX you can imagine enjoying with real time monitoring while a primary mix that's much heavier rolls on?
So, you could take a heavy mix,
bounce it to a stereo track,
drag it into a new project (simplest way to get something with no FX)
and record your lightly effected track in that project...
then drag it back to the original.
Total PIA, but it would do the trick.