I can see it being a handy feature if you have presets you like and would want to use those with a poweramp and cab instead, so you don’t need to go through the presets and toggle them all off manually. So some sort of global cab bypass maybe would be good? However, I’m not sure it could tell if you were to use a capture of a poweramp + cab, plus of course if it’s a capture with a cab baked in it wouldn’t work either.
Also as for routing the same signal to one outputs with the cab and another without the cab while still having post-cab effects, I also don’t think it would save any resources compared to doing it manually, since the QC needs to run two instances of the same post-cab effect anyway, one that has the cab signal and one without the cab signal. There’s really no way around that I’m afraid. So it wouldn’t help much in that case.