Mihajlovic
Its Baltic!
It's doable I guess, but very very tricky... I think he's got a good chance of tying Sampras, but Federer is just out of reach. The good news for him is that Federer isn't really a threat in BO5 (apart from maybe Wimbledon), Murray's not the player he was two years ago and Nadal is only really a threat on clay these days, and no one else is really breaking through into that group yet. But not even prime Federer managed three slams in three consecutive years. And Djokovic will be 30 in three years time - he'll still be a contender then I imagine, but he won't be the same player he is now.
I wonder if Djokovic will have to start sacrificing some of the Masters and inevitably his No1 spot and try focus on the Majors only. He did improve his game a lot and plays more efficient thus not wasting too much energy, but still I wonder as you say how his body will cope with all this in a few years. If he manages to maintain the level of play that Federer has at the moment at the age of 33, I think he will be able to surpass him. I'd say Australian and US Open are 'guaranteed' GS's for Djokovic, Wimbledon and finally Roland Garros being the trickiest...