Man, that is one ugly and amateurish promo video. I'm going to guess that it was done by a GenX slacker who is (commendably) trying to recreate what s/he thinks was the ambiance of the time, and just as Hollywood TV and movies tend to, missing the boat completely.
It does illustrate what I think might be a couple of bigger problems than performer egos. First - the mesh of different vocal and instrumental styles. W5 never rocked hard, but QMS definitely did - and Rush is best-remembered as a blues-tinged power ballad vocalist. Issues there.
Second - to whom do you market this aggregation? Quality older acts from the folk world are having trouble getting bookings - many seem to be resorting to tag-team cruise ventures with other similar acts - and since as you note Bob, this really isn't a supergroup of lead players from those bands - who will want to see them? What kind of venues would make money having them?
Folkies can age and continue to perform with a semblance of themselves in their prime - I've seen John York with McGuire a couple of times in the last 2 years, and they put on a fabulous show - in small venues to small crowds - but rock by its own definition is about sex+drugs+... and in general the youthful spirit of rebellion and self-definition that makes the best rock shows into events that are about the event as much as or more than about the music.
I'm sure you could do the best for them that could be done, Bob, but those are the things I'd be concerned about.