One, Deadpool's always masked, and you kinda have to see the main protagonist's face quite a bit. Even Tobey Maguire walked around maskless in the Spider-Man movies.
Two, a masked person just doesn't work. You -can't- see Deadpool's expressions in film. His smile, his grin, all of that. It just won't work unless it's CGI.
Three, I don't think Reynolds will want to go full-body makeup for any naked Deadpool scenes.
Four, if Weasel ain't in this then I want no part of it.