perhaps we could introduce some other aspects to this suggestion. Maybe have them have a a partial effect on Red and Purples....
Maybe have the Stun disorient and apply a minor slow effect to those of Boss or raid boss status... even a 15-25% reduction of RoAction would be a helpful. Perhaps the knockdown could simply "unbalance" allowing Sneak Attacks all around... for a duration obviously.
I think that the Devs in deveopment of Feats and abilities should come up with partial effects for the "Immune" mobs to make other aspects of play beyond DPS matter a bit more.
I mean for these bosses you can't CC (except with Intim and similar directional aggro control) and special abilities that don't involve direct damage are ineffective.