First off, I'll believe it when I see it.
But, IF this actually becomes reality, there are only 3 guys that would be logical opponents...
1. CM Punk - It's been rumored forever. I don't think Punk would agree to come back unless he was guaranteed the main event at WM31 in his contract against either Ausin or Lesnar for the championship. Punk would of course get a ton of cheers if he were to return, but the one thing that could get him booed is if he went up againt the most popular superstar of all time in Stone Cold. The promos between these 2 would probably be nothing short of epic.
2. Hulk Hogan - It probably should've happened 13 years ago at WM18. For many different reasons I've read, and who knows which is the truth, they went with Rock vs. Hogan and Austin vs. Hall. While it sounds cool in theory, when I come back to reality I cringe at the thought of a 60 something year-old Hulkster trying to wrestle one more time. It's gonna be bad. I mean, did anyone see his last "match" in TNA against Sting? Well take that and add multiply it by 10. Unless Hogan is doing DDP Yoga and miraculously finds the fountain of youth, it's going to be just flat out embarrassing if he laces up the big yellow boots again. Like I said, it sounds great in theory. The buildup would be great, but the actual match would be a joke.
3. John Cena - This one I really have my doubts about, but it is last on my list afterall. First off, I'm not sure Austin would make a comeback to wrestle Cena. Secondly, if Austin comes back, of course he has to win. And I don't think they want to put a loss on Cena's WrestleMania record again anytime soon. Also, Cena is hated enough as it is by most fans over the age of 12. Imagine how bad he'll hear it from the crowd with the boos and "WHAT?!" chants if these 2 were to be paired up.
I'd personally much rather see Randy Orton, Seth Rollins, or even Triple H (but I can't imagine him returning unless it were to face someone he'd never met in the ring before). It would be kinda cool to see Vince return and for him to have a power struggle with The Authority on the road to WM. Vince could lay down a challenge to Triple H at WrestleMania. Triple H laughs and says, "You're challenging me at WrestleMania for full control of the WWE? I'm not gonna fight you, old man." Vince responds, "I'm not talking about me. Your opponent at WrestleMania 31 is going to be...this man..." The glass breaks and the crowd goes apeshit. Just a thought, but again, CM Punk is the most logical choice if they can somehow come to an agreement on a return. Time will tell.