I'm surprised more people haven't followed his lead and lost weight.
Two years ago there were a lot of players that looked like they trimmed down, both on WTA and ATP. Even Fed and Nadal looked slightly more svelt. But also, Kerber, Azerenka, Querry, Stan this year, etc. I don't think it is anything to do with Djo, but just the natural progress of finding the ideal athlete formula for players by trainers and sports medicine folks. Less weight fits both performance and injury prevention criteria.
To me, Djo is too skinny and may lack muscle that can help stabilize joints, but he makes up for it in flexiblity. Only time will tell though.