Well I partially address that here in the post below.
The point is that we don't know how it will work in a 3-5-2. I agree that he plays better with two behind him, which is effectively four as it consists of two midfielders and two centre backs. Here he has three centre backs and one midfielder behind him which is still four players. If the system is played properly then it won't be a huge difference.
The biggest danger is that we start to see huge holes in front of the defence behind Di Maria - but you can get around that by 1. Pushing up and squeezing the space, 2. Having defenders who step out of the back line and make a challenge.
It won't definitely work and no body knows because it's not been tried before. It has a chance of working though so I'm not surprised it's being tried.