Kane, Undertaker, Rey Mysterio, Del Rio, Edge. These are the main-eventers of Smackdown now. I can't really see any other wrestler on Smackdown jumping up to main event status.
Kane and Undertaker. They currently have a feud going that soon I can see the World Title jumping out of that picture. These two will probably go on untill Wrestlemania or even maybe past it. If the Undertaker does retire after wrestlemania then it will be one less main eventer in the picture. Kane may be in the title picture too but It may be a while before he wins the belt again after he loses it.
Rey Mysterio and Del Rio. When Mysterio returns they may have a very long feud. Maybe not of Rey's choice but more of Del Rio's because of him wanting to be the most dominant luchador in the WWE. If Del Rio does not win the belt soon then they might have another feud going into Wrestlemania too.
Which brings us to Edge. He has the ability to win the belt probably in the next PPV if not at most a few weeks after it. If he does He may hold it for a while. The only hard part to tell is if he would turn a heel or stay a face if he feud's with Del Rio. I personally think he will turn heel after he wins the title.
Does anybody remember when Jeff Hardy returned when Edge was the champion and he asked if there were any other challengers since he had beat everybody already? I believe that will be the same thing that will happen when Christian returns.
When he comes back one way or another he has to have a feud with Edge. Hopefully Vince will not screw him out of something he deserves.