Well lets see, we have a worthless crop of players aged 20-23, a rather worthless group of teenagers (the few that exist) trying to make their way on the ATP tour now, an uninspiring junior group. Other than Murray who else is going to win any slams the next 5 years. At some point some new talent (real talent not just a Raonic level who might win 1 slam someday if he is really lucky) will emerge but be prepared to wait a long time since there is no indication there is any on the near horizon and expect atleast 2 if not all of Djokovic, Nadal, and Murray to win ALOT more slams. I guess Del Potro "could" win another slam or two before he retires, but dont bet on it happening either, and dont expect him to win alot of future slams, that is for sure.
The French Open prediction looks especialy right. Unless his body falls off Nadal can win French Opens into his 30s, and when was the least up and comer that emerged on clay of any ilk since Nadal.