Kurt Angle & Jeff Hardy:- These guys could certainly make it, since they have been in the 'E before. When Jeff left, he was white-hot following his feud with C.M. Punk, and, even though Angle has proved to be bat-shit crazy, he would still produce a world-class match. I think, if Angle, came back, he would be on a "Brock-Lesnar" type part-time contract, to keep him from injury.
Robert Roode:- Cert. He looks a heel and carries himself like a superstar. Roode would almost be guaranteed to be picked up by WWE if available, and would even be in the main-event picture at some point.
James Storm:- I could see him being in. He would probably be more a mid-carder, and compete for the IC and/or U.S. Title. He would have to tone down the beer swilling, but the cowboy hat and gimmick could stay.
Bully Ray Dudley-I could see him being a main-eventer, if they use the current BR Dudley in TNA. He has improved his ringwork and stickwork in TNA, and has been a breakout star. Bully Ray v John Cena feud (including Tables Match) -here we come!
AJ Styles-would have to change his name (since WWE already have an AJ). I could see them changing it to "Styles" and a nice touch would be to have Joey Styles manage him. Might be given a run in the mid-card, but I can see WWE running out of ideas for him.
Bad Influence-Could be in as a tag-team, then Kaz will get buried, while they put Daniels in a feud with Daniel Bryan. Daniels may be buried eventually, but would be kept around, due to stickwork and being able to generate heeel heat, as a manager or commentator.
Sting-Won't join, but would love WWE to offer one-night deal to Sting, for massive money, to headline Wrestlemania against the Undertaker, especially if it is Taker's last match.
Austin Aries-Too much on the mike like heel C.M. Punk. Maybe WWE could have him do a feud between Aries and C.M. Punk, now that Punk is face again.
Mr Anderson (KEEEEENNNNNEDDDDY)- Limited value, but could come back by taking out Randy Orton, who he blames for getting him fired from WWE. Also, never had a feud with Cena, so there would be some freshness there.
The Knockouts
Mickie James:- Could come back and be a hit. "Hardcore Country" could be her new gimmick in WWE. Would give cred to an ailing Divas Division.
Tara (Victoria)- Has been in WWE before and had success. She, too, could get a push, since she was over in her previous stint. Works better as a heel IMO.
Velvet Skye- I am surprised that she has never been given a contract, as she is hot, popular with the crowd, and can actually put together a match.