Rafa will only improve physically from now on, his knees getting stronger with each match. He is just in his first phase of domination on clay, he's about to enter the second phase of his career where every win on clay will be in straight sets with Rafa never being broken. You can expect another 4 RG-Wimbledon doubles. He will also start his domination on HC and indoors, and by the end of this second phase he will be known as the indoor GOAT. This second phase should start next season and will likely last 5 to 7 years, featuring 3 more titles at both the AO and USO and a 6 year being undefeated at the WTF. The third phase of his career will last for another 10 years after that, years during which Rafa will only win 2 slam titles a year, but he'll still remain #1 in the rankings based on his record setting 10 straight seasons with 8 Masters titles. Not counting his 3 additional Gold medals.
Nadal is past the midpoint of his career.