AJ Lee is one of those "what ifs" in the WWE. That promo she had against the Total Divas in 2013 was great. She as by far the best wrestler in the WWE at a time when the Divas Division at the time was at an all time low. She debuted during the latter stages of the Post-Trish/Post Lita Era and by the time she established herself as the best on the roster, Mickie James, Melina and Beth Phoenix were already gone and outside of Natalya, the talent was mediocre at best when she ruled the division. Her feud with Paige was good but I think by that time, she stopped giving a damn about the WWE anymore. I wasn't surprised in all honesty that she quit the WWE a few days after WrestleMania 31, I was surprised that she quit pro wrestling in general though as I would have thought that she would show up for Shimmer or Shine.
I know it's "never say never" in the WWE and in pro wrestling, but I think it's safe to say that we'll never see AJ Lee in a WWE ring ever again. I could see Beth Phoenix and Mickie James back as WWE Ambassadors and I could see Melina back in a similar role someday, but to me, AJ Lee is a never.