I honestly dont understand why u wpuld remove it? Its like a perfectly fit protector u never bought :P
The surface of the glass under the plastic film is not as smooth as other phone screens. I think this is because it is not intended to be used without a film above it.
I removed Sonys plastic film and added Orzly Tempered Glass Screen Protector (you can use any other tampered glass protector). nearly perfect for my and much more scratch resistant than with the plastic film.
So a glass back would be a neat feature.