I don't think the SL version was nearly as popular as the mesh version. Owning both an SL and a mesh, the SL is very stiff on the toes compared to the mesh and also does not breathe well. There's a clay Vapor 9 out at the mo which is SL to keep the clay out of the shoe, but every other retail version is mesh this year as far as I've seen. Fed didn't actually even use SL upper at Wimbledon last year, he was using a mesh upper. The only time he uses SL is on clay surfaces to keep the clay out of his shoes.