Hard to tell . I guess this is not gonna happen recently and imho it also depends on the timing.
So apart from J'torian who apparently seems determined to fight for it , From the older generations , i guess Gonzo can get a chance if he manages to keep his level constant and from the younger generations :
Murray seems qualified talent wise though he's not yet in it mental or physical wise. I am far from being a fan of any of them but Berdych and Djokovic may be qualified regardless of the eventual drop in their games and thinking . Nadal can manage to do it if he manages to keep some distance between him and the other guys but still i don't think he has got the biggest chance here. At least Not until he finds some big answers.
Any how i guess after Fed. the number one ranking may be rolling faster between players regarding their close levels ,but who knows what'll happen.