Djokovic is playing at the highest level I've ever seen since I've been watching tennis. The only option is for him to have an off day, a super tennis talent emerges, or his window closes as happens to everyone. Other than that, at this rate, Djokovic can overtake Federer and Rafa. It is within his grasp and if things continue as they are, it will take two and a half years considering that he has two off days at the majors.
Credit where credit is due. Novak has raised the level to a level unseen before. He rarely misses, he understands the geography of the court, he's fast as lightning, and his mental strength is now off the chain. There is no hope for the others outside of Novak being under the weather, IMO. Sadly, Novak has already announced his intention to go after Federer's haul of majors? Who's going to stop him?