I personally think Andy's back injury is being either overestimated or underestimated by fans given their respective perspectives on the matter. And I don't mean masterclass by that. I think he's asking the right questions. Since we have no idea to what extent Murray's back injury was therefore, the surgery, we can only speculate so much.
As to young guns, I think both Dimitrov and Janowicz have done well considering but I believe it's Dimitrov who's going to take things to next level. JJ still has a bit of process to go through. He still hasn't been exposed to everything. There are still many missing elements as far as the whole picture is concerned. Raonic is already there so he might just become one of the main contenders at the Slams. He's been exposed considerably and has the right kind of experience by now.
Nole, I believe, will keep his consistency alive and will keep his stakes high as usual. I also believe he'll be very hungry for AO given that he'd been denied 3 Slams since last AO. He is and will be the man to beat.
Nadal, I feel, will have to rely on a good draw to make the AO final. It will be interesting to see how he feels after the long season this year. Fitness therefore confidence is the key to his winning streak.
Del Potro should take over Ferrer and should be able to do more than he does next year and same can be applied to Stan. I will throw Berdych in this mix as well. He didn't have a very good year this year but that can always change.
Federer, of course, is the dark horse. He had a really bad year this year but that is to be expected at this stage. Now that he is without a coach, it will be interesting to see how much can he hold on his own going forward. Even a new coach won't be as promising as the problem is not with the coach but Federer himself.