It would be a good fight, but Henderson needs some more wins at LHW. He is fighting Bisping at MW so it wouldn't happen for awile. I don't think Rashad will be champ if Rampage gets a title shot.
I think it has a chance in a non-title fight. But I can never see a five round fight between them.
In a three rounder, i'd take Rashad. But in a five rounder Henderson would have a better chance. Both great fighters and it could go either way.