He is almost branded to TNA. In other words, when I think of TNA, I think of styles, angle, and sting (In no particular order.
Another thing about him though. His ability to create 5 star matches out of nowhere is unbelievable. When I watch iMPACT and I see Aj styles make an entrance, I know for a fact that the match up next is going to blow my mind.
Would he fit in the WWE: no! No! No! Because I doubt Vince McMahon would let him keep his character, and WWE's safe style of wrestling (limiting people's move sets) would see a restricted Aj styles wrestling with an unentertaining gimmick. Plus, there is no x division/cruiserweight division in the WWE currently, and some of aj's best moments come from versing the x division.