Nadal is 27 years old. Considering that it's unlikely Federer win another grand slam title in his career if Rafa manages to emulate Roger's gs record from 27 till 31 we're talking 5 more titles. That would tie their record at 17. If he manages to surpass it he will go ahead in the tally. What happens to the GOAT discussion then?
He should ask his knee first.