I've never been in love with this tourney for a variety of reasons.
What changes, if any, would you make?
Would you keep the RR (group) system, go to a standard knockout draw, or modify it otherwise?
Keep it to 8 players or expand the draw?
Change the surface or conditions, or keep it (at least roughly) as is?
the general main problem with a 16-player KO is that there would be few easy R1-opponents to get into the tournament.
that could lead to R1 upsets by BautistaAguts.
the traditional RR format somewhat protects the top players or at least keeps them on stage.
the YEC is designed as a showcase to an extent ...which might be matter of taste ...but a 16-player KO would definitely be worse and even a 32-player KO would still be risky.
a solid alternative (and something i might like) would be to completely cancel the Bercy week and have a 64-player indoor YEC (worth 1500 points) instead (of both).
but that would be yet another KO tournament then.
the traditional YEC, despite its issues with the RR, lightens up the calendar.
also, in a Grand Slam it time and time again happens that one finalist had a cakewalk inclusive a walkover, while the other got the draw from hell and is simply tired or even injured in the final (as Best-of-5 is so tough).
at the end of the season, the likelihood of injury tends to be higher, but in RR it's easier to enter a substitute.
Best-of-3 indoors is not so gruelling also.
as for the YEC RR rules, the task is basically: win your matches and you will advance, or if you lose, at least win a set.
so Nadal's current situation is not so crazy.
personally i still don't particularly prefer the RR ado to mentioned 64-player Indoor "Slam"(Bo3).
as for surface changes, erm, well, how should that be materialized in any sensible way?
indoor clay? Asia? that's a topic for a separate thread, i'd say.