First of all, he's only number five, not even number two or anything. Secondly, he's NEVER going to be able to do what Roger or Rafa have done.
A( because they are legends.
B( Cuz they are teh only two consistent players on teh ATP tour.
C( Because Roger is tough to beat and Rafa is teh only eligible man to be teh next number one.
Novak Djokovic will definitely be the next number one. After Roger and Rafa retire, that is.