Craig Anderton's "Quadrafuzz" works kinda like this (as does Crysonic's Spectralive NXT plugin to some extent.)
Quadrafuzz was an interesting idea that hasn't been fully exploited, possibly because it's a bit complex for the user. The idea was that intermodulation distortion could be reduced in this fashion, bringing you closer to the sound of harmonized fuzz guitars only without having to multi-track anything. Perhaps in the future we could see "plug in packs" for the KPA (ala TonePrint/PodFarm) or even 3rd-party plugins (ala TonePort), wouldn't that be a hoot.
But if you're thinking more about blending discrete sounds/amps, I'm all for that. You can layer up two amps in a number of modelling products, for example. We have the "Clarity" knob, which was a clever touch by CK but not in the same league. In my own studio I have a pair of overdrives that I run through an Xotic X-Blender; I can dial in either one or both, or even dial in just one and mix it with dry. It's a real problem solver.
-djh
This post has been edited 2 times, last edit by "dhodgson" (Mar 15th 2012, 2:54am)