This wimbledon marks the 10 year anniversary of federer so it has some added meaning to the drama going in.
Im excited but sad at the same time. Last year may have been the last time federer could have beaten nadal on grass since he was serving very well and since has decompensated because of the back.
Wimbledon will reveal if there is anything left in the fed-nadal rivalry. If fed had to pick a venue playing nadal at a slam event in 2013 with the conditions that exist he would pick wimbledon, quarterfinals arguably being better for him with the grass in better condition than say the finals. Also, nadal may not be at his most comfortable at that point. So if this were an outdoor wimbledon final in 2013 i would say nadal in 3 sets pretty easy given his comfort at that point of the tournament, the court conditions (borderline clay court), and fed being maybe tired with a hard semi before the final.
The quarters will at the least give fed fresher grass, less chance of fatigue, and perhaps a less confident nadal as that would be his 5th match vs 9th match this season on grass. Even then I would give federer a set at most.
The only way federer has a chance to win this match is if it rains and there is a roof for the match which eliminates the elements, adds humidity making the ball bounce lower and i believe the court is sliplier due to more moisture and thus less defense can be played on it. Even here fed would have to close it out in the 4 sets as he will lose if it goes to a 5th at this point in his career.
The sad part is, if fed cannot beat nadal on grass at the quarterfinal stage in what most likely will be an outdoor match not only does it mark the end of the rivalry between these two it ultimately marks fed ever beating nadal at a slam again and then fed will have to hope nadal and him are ranked 3 and 4 and someone else takes out nadal in the future. 10 year anniversary could be the final nail in the coffin for the fed-nadal rivalry and its a sad realization but that is the life of sports.