I don't know if Nadal can win USO next year because of the USO curse and all where nobody in a decade has managed to defend the title there. But I think he probably has 2 good years left of having a shot of adding another USO title. The competition will be much tougher though and he'll need a very favourable draw where he'll need to be fully fresh mentally and physically. I can't see him going through Thiem and Medvedev and Del Potro back to back back or going through Stan and Dimitrov and Djokovic back to back to back if you know what I mean. That would require a superhuman effort. But if he gets a great draw and only plays maybe 2 of those guys then he has his shot. This year's USO was a very good draw for Nadal. Even then he barely made it over the finish line. So yeah..again some luck will be needed and hopefully Nadal will stay in good health as he's a crucial part of tennis' popularity. I feel the Federer fans will become huge Nadal fans and the Nadal fans will love Federer a lot more when both Federer and Nadal are gone and everyone will understand how special their rivalry was and how supremely talented they both were. I don't feel Medvedev, Thiem, Tiafoe, etc will be getting that same fan following when they're at the forefront.