Seen as I made this thread, I thought you may be interested to hear my opinion(or not):
CM Punk - More than up for the job of main eventing mania in my opinion. Assuming he's not locked in another entertaining yet pointless mysterio feud like last year, he is quite an obvious choice.
Wade Barrett - Although he is fresh to WWE and the main shows, in a short amount of time he has more than proven his worth as the centerpiece of nexcus, wihtout which it would fall apart, and a future main eventer. If sheamus was the break-out star of last year, berrett is that to this year. And with plans of having nexus around til WM it is ever the option.
JOMO - His push is so timely and personally I think he could set up the best possible scenario of a storyline at WM. Picture Barrett at that time holding the title, no other guy would lose to morrison this early in his push. You couldn't picture cena or orton or even sheamus losing to him actaully at WM. So he beats barrett and miz cashes in on morrison and it sets up a 6 month feud (very very hopeful I know). Not to mention the fact he has the ability to make a royal rumble win look very convincing and deserved.
All of those guys saying christian are more of a dreamer than TOMMY himself. I also think any guy who has been in the company for less than about a year won't get it. So I'm ruling out bryan, all nexus guys 'cept wade, kaval, del rio and any others because I just don't think that any guy would be pushed enough to main event WM within their first year. Looking at history, not even guys like angle, sheamus, lesnar or any other huge stars with the most amazing debut years have been granted that privelige so it seems impossible to me.
I don't consider the miz a possibilty because there is no point, he has MITB already! The only way i could see him winning it is if he is unsuccessful in cashing in the briefcase before the rumble. As a matter of fact if he failed to cash in on the same night previous to the actual royal rumble match up, it would set up WM flush for him. But if he still has the briefcase, he aint gonna win royal rumble, thats putting too many chips on one guy.
Either HHH or chris jericho has a great chance if returning but that would just fuel the fire of another thread I posted which is why I don't want it to be either. I suppose has a pretty good chance, he's been proven a great competitor now and has one successful wrestlemania high profile appearence under his, rather revealing tights. Kane won't win rumble same reason he neevr won MITB, it isn't very kane to win a royal rumble, he doesn't need to do that when he can get himself into great little feuds and a place at the grandest stage without winning one of those things.
I actually think that edge has a great chance if he loses to kane because he's never won the rumble and it's a great oppertunist type of thing to do. It would also be perfect because he could go out with 10 world titles under his belt, no pun intended. Taker won't be ready for rumble. Orton is another good call if he loses to barrett because it could set up a great match between the two or himself and cena which is surely wrestlemania worthy stuff.
But the three guys I named at the top I reckon have the best chance. The most to gain, the most likely, just the most fitting guys I can think of.