I think only the heat and humidity can beat Djokovic at this point. Millman did well against Federer but Fed absolutely gifted him so many points. Can't see Djokovic doing the same. Haven't looked at the draw properly - could Rafa and Novak meet in the final? That could be epic given their Wimbledon match.
I love that the 'old guard' are still competitive but I would really like to see some of the new guys start winning slams. Thiem played well but I never really believed he would beat Nadal. Great match though, and I think Del Potro will be a big challenge for Nadal!