RG really is Rafa's to lose until his body gives up on him. He's lost one set in his last 14 matches there. He could conceivably keep winning it until he's 36, which is another 4.
There is a rumour going round the Tennis circuit that this year will be his last Wimbledon as his knees can't take the back to back RG-Wimbledon despite the now 3 week break between the two tournaments. His record at Wimbledon has been pretty poor since 2011, so it may not be so far fetched. So, in future he would save himself for the USO, which is slower and higher bouncing.
Next gen have been a little disappointing and haven't yet broken through at the Majors. Zverev has only got to a quarter final of this slam. Thiem was in his first slam final v Rafa and even his game is pretty limited and he's only a factor on clay.
Novak - went out early and seems to be going through a similar slump in form that Rafa faced 21015-2016. I'm sure he can come back because he is the only one with the game to challenge Rafa at RG.
Roger - back for the grass season after his mini sabbatical. Hope he can win a few more slams starting with Wimbledon next month.
Murray - Keeps deluding himself or playing games with the media with his come back from a pretty big op on his hip. Even if he does play at Wimbledon he's unlikely to last the first few rounds because he just won't be match fit.
