I'm really surprised the younger generation haven't reached more semi-finals or later in Slams. Thiem is the only exception but he's still an incomplete player, enters too many tournaments and still can't quite get the balance right between risk and percentage play. Still, Nadal hasn't been convincing so far so he may have a chance. At one point Dimitrov looked like he would become a contender but has fallen away again mentally. Zverev still can't do it at slams and Kyrgios doesn't seem to care enough. If anything it could be the likes of Tsitsipas, Coric and Shapovalov that could break through when Fed's retired and Nadal and Djokovic are in their twilight years.
I'd love to see Del Potro win the tournament. He's played very well and spent very little time on court so at least he'll be fresh against Isner. Beyond that unless Nadal improves he could reach the final where he'd have a chance against Federer but very little against Djokovic who has always been a bad matchup for him.