El Dude, my apologies for any confusion.
If we could categorize the chances as practically no chance, small chance, fair chance, good chance, excellent chance, then let's say at least a fair chance.
As an example, at his best, one would probably say he had an excellent chance to win three of the four with a small chance of winning the 4th - because of one player's dominance. I don't think this is the case anymore, but he could prove me wrong.
I couldn't put each chance level for each major in the options, so that is why I'm saying at least a fair chance.
Let's see, my opinion if I were to break it down:
Australian Open - fair chance - Draw has to open for him somewhat, because by the time they get to the semifinal, all matches are at night and the court is pitifully slow, but still bounces relatively high. He has almost no chance against Nadal or Djokovic unless they are playing poorly. Against Murray is a better chance, especially in the upcoming year because of his time off for surgery.
Roland Garros - small chance - Rafa is still playing well, and at this point Federer is probably better off for Wimbledon not going deep at Roland Garros. However, if Rafa were to go out early, it might be incentive to put in the effort. Federer has been the second best at RG historically, even if 2012-2013 didn't reflect that. In 2012, make no mistake, Federer had Wimbledon as the goal, squarely in his sights, and would not risk it trying to put in a big effort (play long points) against both Djokovic and Nadal at RG. In 2013, Federer was clearly on a working vacation.
Wimbledon - still an excellent chance when healthy - Throw out the Stakhovsky match. There is no better player on the grass today when Federer is anywhere near his best, other than a freakish performance, like Tsonga of 2011 where Tsonga played an otherworldly level, especially on serve for the last 3 sets. Murray would also have an excellent chance of course, but I'd put my money on Federer if they were to meet in a final as long as his prior match was not too exhausting, like his 5 set with 4 tiebreakers equivalent match against Del Potro in the Olympics; pretty tough on a 31 year old to recover to play a player of Murray's caliber. So hopefully for both, they are not on the same side of the draw.
US Open - good chance - as others have stated, there are enough players that can play a high enough level on for a single match to give Roger trouble in the present conditions on Arthur Ashe Stadium court, which has definitely been slowed over the last few years in my opinion, along with most of the other hard court tournaments. Players that used to relish the previous medium-fast conditions no longer do as well there, and players that used to barely reach semifinals are doing better. If they would stop putting so much sand or grit in the paint they use, players like Djokovic wouldn't be able to slide on a hard court like it was clay because of the level of sand/silicate in the top layer of paint, which creates more friction and slows play down, especially with certain types of balls.
Respectfully,
masterclass