In all fairness the court is faster and slicker, and in all fairness Federer never once won Wim. when it was fast and/or slick. Federer grew up a clay court player, also Federer gained his best result not until the courts and/or balls had been slowed down.
Look no further than WTF where the court is extremely slow for a hard court. That is where he is absolutely the best, not having to deal with outdoor conditions is a huge plus for him as well.
I don't believe that Federer is finished until he can no longer win or runner-up at WTF. Same for Nadal with the FO, however I think it is possibly the end for the both of them.