My personal favorite supergroups are LTE and transatlantic. I think Steve Vai's band could be considered a supergroup.........i mean come on, Vai, Sheehan, Macalpine, and (for a short time) Donati in one band? Count me in. The guitar trio is pretty badass too (al dimeola, paco de lucia, and john mglaughlin).
For those who say Vai isn't creative, sorry...........but you are deaf. Thats fine if you don't like him though.
I also don't think being able to read music is that important for fitting the criteria of being a virtuoso. I am a huge supporter of being able to read music and learning theory, etc. I mean somebody can be the best player in the world, but if he can't read and goes to sit in on a jazz gig or something and they put a lead sheet in front of him......guess who isn't playing a second gig. However, take Joe Pass for example (one of the greatest jazz guitar players of all time for those of you who aren't familiar)........the man couldn't read and knew practically no theory at all, and he is still one of the most revered jazz musicians of all time.