CAMELOT FANTASIES

You're right general.  Who can stop him in 5 sets? 

An aging brilliant Federer? Clearly it's very difficult for him to keep mentally focused for some reason in a 5 set match. Yet rather sadly, he is the only one giving Novak battle most recently. Well, Stan as well, sometimes.

Nadal?  Well, I still think he has 1 RG left in him, but I don't know if he wants it badly enough.  He must realize the window is quickly closing.

Murray?  As you said.  Lacking in areas.  Forehand, weak 2nd serve, and a bit of a mental thing with the top players.

Wawrinka? Ok, his best level matches up well with Djokovic on the slower courts like AO and RG, where he beat Novak this year.  But you never know if he will be there at the end of a tournament.

Nobody else has challenged him.

Unfortunately Del Potro seems to be permanently injured with the wrists.  I hope not, but it's not looking good for him.
I always thought if he could be healthy he would be there with Novak and Andy once Rafa and Roger diminished.

Cilic may have been a 1 timer and he is 0-14 vs. Djokovic anyway.

The generation following Djokovic, Nadal?  Like Nishikori, Raonic, Dimitrov?

Nishikori, maybe, but he seems too brittle and prone to upsets.

Raonic, no. Dimitrov, looking less likely as time goes by.

The rest just don't seem slam material, and they are hardly competitive with the top players.

The younger generation of Kokkinakis, Coric, Kyrgios, etc.  Maybe, but it will be a few years.

Really right now, it should be Nadal & Murray who should be Novak's main rivals.  But neither looks up to it at the moment.

Let's see how Novak does next year.  He'll be 29 in May. 
But he is so fit, I think it won't matter with the lack of competition. 
He could win 3 of 4 next year or even 2 years if he is still motivated.

Respectfully,
masterclass