At one time I enjoyed Mr. Kennedy and thought he had loads of potential. Over the years, and throughout his time in TNA, I've come to realize he's really nothing special. Don't get me wrong, I still think most who bash him underrate him greatly, but he really is just an average wrestler, with an average look, who is GREAT on the mic.
Now, mind you, if he wasn't injury prone or a liability in the ring because of a lack of skill, I think he could've taken that great charisma and mic work he has and become something big. Lots of wrestlers with little in ring talent but lots of charisma and personality have. Unfortunately for Kennedy his weaknesses have been flaunted too much and stood out too great and he's unable to get past them now.
I think part of his problem in TNA has been poor booking, though, as well. The guys a great, natural heel, and he should remain as such. But instead TNA just jumped back and forth with him so many times, because of horrible booking decisions and a lack of direction, that no one gives a shit anymore about Kennedy.
Back to the thread topic, though: I wouldn't care either way about Kennedy returning to the WWE. I think it's entirely impossible now, though, and will never happen. WWE could forgive past heat and problems, but only if they thought the talent would offer their roster something. Kennedy doesn't really offer anything at this point, so they have absolutely no reason to be interested or desire to bring Kennedy back.