Obviously it is a possibility that Bray Wyatt could be a potential opponent for Sting, but it depends upon a number of factors. First and foremost, of course, it all depends on if Sting has any interest in wrestling anyone in a WWE ring, or if WWE has any interest in having him compete. It's quite possible that he is there only to hype that game, prepare for an induction into the Hall of Fame, and possibly appear in a non wrestling capacity only, whether it be in ring or backstage.
Assuming the plan is for him to compete, it all depends upon when he signs and for how long. If he only plans on wrestling in one match, and that proposed match is at WM31, there's no way in hell it is against Bray Wyatt. If that's the scenario, his opponent will clearly be a more legendary opponent, such as Undertaker, Triple H, John Cena, or CM Punk.
If he signs more recently, and has a warm up match or two before appearing on the grandest stage of them all, there's no doubt Bray Wyatt could be an opponent, someone who he would beat, but Sting could make him look like gold in the process. Or if he plans on fighting Taker at WM31, and sticking around beyond that, again, Wyatt would be a great choice of opponent.
Personally, I still think the best opponent for him would be the Undertaker, even though the streak is over. Sure both guys are older and beyond their physical primes, but there's no way these guys couldn't pull off an excellent match which would be more about the spectacle than it would be about the quality of the in ring action. People talk about Sting like he's a decrepit old man which is a gross over exaggeration. Obviously, he's not going to sign on and wrestle every week on RAW, traveling all over the world in the process, but he can definitely come in and pull off a more than plausible match against a dream opponent. Likewise, no one is going to ever convince me that the Undertaker was so decimated by his defeat at the hands of Lesnar that he cannot compete 12 months later. I don't care what current reports of Taker's physical status say, WM31 is still 8 or 9 months away, and he can definitely get his act together well enough by then to face off against another legend.
So yes, Bray Wyatt could potentially be an opponent for Sting, but it will all come down to logistics and timing, with the Undertaker being the ultimate goal. But Wyatt could definitely be a plausible warm up act, or a nice follow up opponent.