I'm going to assume this thread is refering to wrestlers who haven't won the World championship yet and will become the champion and reach the main event in 2012. That's at least what I'm going to go with because there's plenty of obvious names who have been in the main event scene for years and will continue to be.
I really think Dolph Ziggler is a wrestler who will finally get a chance to be World champion in 2012. I know, technically, he's already won a World title. But, fact is, that was such a short and insignificant reign that I barely count it. I think 2012 will be Ziggler's break out year where he's actually given the title seriously and he's given a chance to stay in the main event scene. He definitely has the tools for it, although I'd prefer if he dropped Vickie Guerrero and got away from her before becoming a real heel champion. I'm tired of Vickie Guerrero's involvement, personally, and I don't think Ziggler needs her anymore.
I also think, if they continue to book Mark Henry the way he's been booked the past few months and continue to push him as this dominant, frightening heel, then he could easily be a World champion and have a good run. He's looked great during this run as a heel, and while he may not win the title from Orton at NoC I do think he could easily be a serious champion and main event player in 2012.
I also think Wade Barrett, Daniel Bryan, and Cody Rhodes are also likely names who could step up and be World champion sometime in 2012. I definitely think Barrett should be given the shot and a run in the main event this next year.
Personally I would really like to see names like Christian, Sheamus, Alberto Del Rio, and even Jack Swagger, who have already been World champions, either return to the main event scene and be developed better or stay in the main event scene and be given more opportunity to be stars there. Especially Christian!