The Tanker is already strapped for Endurance, unless you go the whole Fitness route, which takes up a lot of powers that could have been used on Tanker powers instead. Putting an endurance penalty on Rage would be disasterous for lower and mid level Tankers. The current system of having you get stunned after it drops is harsh but can be avoided, as stated multiple times in previous posts. Any penalty to this power should be token, that is if the Devs are REALLY interested in inproving the Tanker, which they SHOULD! (I don't see how the changes to Invincibility have accomplished that though. Haven't they done the exact opposite?) I don't like the idea of pulling over a power from another powerset to replace Rage. Keep the SS Tanker unique. In my opinion, the Tanker is STILL below the other Archetypes and any changes should be to make them better, more damage dealing, and more useful.
I especially oppose any change to the Tanker that makes him more dependant on teaming in any way, shape, or form. You should be able to play his game solo from lvl 1 to lvl 50. Not everybody likes teaming and being pressured into teaming is a sure-fire way to drive some players away.