How can someone who bailed out from FO (one famous doubles player said Fed was scared), and didn't play for couple of months, be overwhelming favorite against Nadal who is on fire right now ? Especially if Nadal takes RG, Fed has slim chances to beat him on grass or hard courts.
Nadal could easily have 16 Slams before UO, and this would make tennis exciting, not to mention Fed becoming nervous again.
Because Nadal has been booted out of Wimbledon in the first every year since 2012, whereas Federer has performed well there every year, even when he was injured last year. Plus, Federer has extra time to practise his grass court game, which Nadal does not have the luxury of.
Also, didn't Nadal bail out of Wimbledon last year? That means he hasn't played a match on grass in two years. We will have to see how he does at Queens first.
Federer's time out is irrelevant to the USO because he is expected to play most of the big events following RG, and AO, IW, and Miami would suggest that Federer is currently enjoying this matchup far more than he has historically.
As much as I'd like to see Nadal complete a third channel slam, I don't see it happening. The best, most realistic scenario right now is Nadal sweeping the clay, and some of that could depend on how long it takes Djokovic to get out of his post 2016 CGS slumber. If Novak gets booted out early at Rome as well, then a clay sweep is a huge possibility. If Novak beats Nadal and makes the final / wins the title, then La Decima could become a 50-50.