Round Robin really sucks, I totally agree with Federer.
Double Elimination would be nice! Just like this
For Example Federer, Nadal, Djokovic and Murray lose in second round, bad day!!! but... in this case all of them have another chance... playing in one loss bracket... For example ... in the case Murray loses another match again then he goes home ... but winning he would be safe... cause One loss bracket winner meets winner bracket winner and the winner is the champion.
anyway... this wouldn´t work in Grand Slams only because a matter of schedule.
But it´s a good choice talking about Miami, Indian Wells or Master Cup.