He could, but I doubt it. He is not even close. No matter what he'll retire as one of tennis legends and I'm happy with that.
To have played and competed well against Roger and Rafa in itself is big. Novak will figure in most people's list of best players ever . He may never reach the status of being the "greatest" on any surface> He is sure to end up with the Player with the most Titles at the AO. He will get his 5th AO title in 2014 /15.
I do not see Novak winning Majors beyond 2015 . He still has 10 more Majors till USO 2015 where he can make add to his current tally of 6 .