I think there was an extensive thread about linking speaker impedance curves to IRs, which would of course mimic the real world the closest way, but I guess the complication comes in that so many IRs do not have equivalent impedance curves in the unit, and it's really more a function of how the power amp reacts to cab. I'm still advocating for always creating custom ones; it's so damn powerful. I do think it would be awesome to be able to link automatically at least Factory IRs or have a tagging system that uses key words to link IRs with key terms to impedance curves. But at least having the global setting recently introduced helps tremendously. Saving custom curves would also be awesome.
I hear what you're saying about combining two of them though; interesting concept, really pushing beyond what could be achieved in the real world; very cool.