Raids should stay within respective class. A player in diamond class should not be permitted to raid someone in platinum and so on and so forth.
This is a good idea, in theory. In practice, though, there are too many changes. It could block many revenges as players change from one arena to another almost daily
Expanding on @Nightmare21 suggestion, only the roll algorithm will be affected, limiting new raid roll to only attackers raid platform, but once you have a pending revenge, it should allow.
Thank you for participating in the forum.
Math is boring
For some boring links about how this complex math works
([FAQ] What contributes to trophy inflation in top alliances? How do Zombie accounts effect trophies? How do you gain trophies? What happens with trophy dropping? ( includes Giraffe/ Human hybrid example ))