Federer will be 31 for three of four slams next year. He is old enough, in tennis terms, without people talking his age up further. As for his chances, I think the should be good. Next year he'll have an entirely free hand to play what he wants. It is not far-fetched to see him giving less priority no #1 now that he has got the record, focusing fully on the slams.
Actually that's a good point, I had overlooked the fact that Federer can cherry pick the tournaments he wants to play in.
A bit of a disadvantage here for Nadal. Maybe the rule should not be based on age, but by the number of matches played on tour.