So, as we know Federer rose to #4 and Nadal to #5.
What are the chances Federer will still be in #4 by the start of RG, given he won't be playing in the clay-court season?
Fed will drop his Monte-Carlo QF, taking him to 5125 points, 390 ahead of Nadal. I believe Wawrinka is guaranteed to be ranked ahead of him at the FO, no matter what happens.
Rafa has good clay-court warm-up results to defend from last year, with wins in Monte-Carlo and Barcelona, SF in Madrid, and QF in Rome. So, he'd have to do something like W/F/SF in the three MS, and defend Barcelona, in order to overtake Fed. He's not done this since 2013, and while he's clearly doing well, I am not sure that he is playing quite as well as in 2013. On the other hand, it is not clear how well his main opposition will be doing either. So he's certainly capable of it in principle, but it's hardly a given.
(On the other hand, he is very likely to be ahead of Fed in the rankings after RG.)
I don't see anyone else likely to overtake Fed. Raonic has never had that much success on clay, while Nishikori has a fair amount of points to defend already.
So I'd probaly put it at at least 50-50 that Roger may get a top 4 seeding for Roland Garros. I would have never thought that was remotely possible, even after his AO win.