Is it possible to have material mix elements in the same way you might have lightmix?
Like multiple material options rendering at the same time that are visible within the VFB. I understand it would mess with the GI scatter but would that be contained within the material pass itself?
Just a thought 
I saw that colima program for vray a while back and it looked pretty useful for quick variations.
It is not impossible, but I don’t think this is something we could achieve in foreseeable future.
No problem, i didnt know whether it would work in a similar way to the multiple HDRI setup in V4