I think he has a real shot at it.
This may be the easiest year to achieve something like that (for the top player of the era, now Djokovic).
1) There has never been an era in tennis where the four GS had such similar conditions as they have today.
2) There has never been an era in tennis where everybody played basically the same style as they do today.
3) The only reason Federer didn't win the Calendar GS was that Nadal was almost unbeatable in RG, but now we really don't know what level will Nadal be able to achieve again if he comes back. So in the moment Nadal declines (and I think it has already happened), the best player of this era (now it is Djokovic) has a great chance to win the four GS in the same season because there won't be a Nadal to shut the door at RG.
4) In this special homogenized era, the only thing that can stop the top player of the era is another one of the top-4, but now Nadal is missing in action, Federer is not at his best anymore and so you have almost only Murray to stop Djokovic. But Murray is like a clon of Djokovic, only that Djokovic is a bit better.
5) Djokovic biggest problem may be Wimbledon, and that is because he doesn't move there nowhere near as good as he moves on hard courts. If Djokovic learns how to move well on grass (he could try to learn it from Federer and Nadal, the two best movers on grass from this generation), he could win WB again this year.
But the funny thing is that it is not that simple. Nobody knows what will really happen, and perhaps it will surprise us all, maybe the most unthinkable things could happen this year.
We will have to wait and see...