There is absolutely no doubt that there is a demand for Sting in WWE. Maybe it's nostalgia. Maybe it's simple curiosity. Maybe it's the people who are truly fans of his wanting to see him have one last run, however brief, in front of an audience on the grandest stage of them all. Hell, maybe it's a combination of all of this. But make no mistake about it, the demand is there.
I'm not so sure why people think he will be in terrible shape. Granted he won't be 1990's Sting, but he's had sufficient time to get himself back into reasonable shape for a man of his age. And the spectacle that will surround his debut, plus his ability to tell a story in the ring, his charisma, his mic skills, etc., will make his appearance more than plausible and entertaining. And I don't mean just one match at Wrestlemania: there's no reason to think he can't come on board for a year and compete several times on a few of the bigger PPV's. Clearly he won't compete every week on RAW, and won't endure the rigorous WWE schedule. But he can clearly do a Lesnar-esque schedule, easily.
I also don't buy the fact that no one will know who he is. That's nonsense. There are a lot of folks in the audience, whether it be in the arenas, watching on TV or on PPV, who are old enough to know exactly who he is. Those who are younger have parents, or grandparents, or older siblings or family members who can damn well tell them who he is. My son is too young to have seen Sting in his heyday, but I can assure you, he damn well knows exactly who he is, and he will be high fiving me when Sting walks out on some episode of RAW. And I doubt he's alone in that regard.
Plus, there's this new fan dangle thing that the younger generation seems to like. It's called the Internet. And on there, there's plenty of opportunity to go online and find plenty of footage of Sting from his prime. There's no reason to think that if WWE promotes him properly, which they seem to be doing, that the younger generation will be unfamiliar with him. It seemed to me that people knew who the Ultimate Warrior was. And they'll know who Sting is too. And they'll appreciate seeing him. Not as much as they would have 5-10 years ago, versus the Undertaker with the streak on the line. But there's a demand for Sting in WWE, I'm convinced of this. He'll be far more motivated than he was the last few years for obvious reasons, and the results will be there, count in it.