Better than HD? I doubt it. There's no way that the Model S screen is 1920 across. Probably more like 1024. So instead of 1920x1080 you'd probably end up with 1024x576. Playing video is no problem, even the POS Kenwood that I've got in my Roadster can play videos off of a thumbdrive. I'm sure that the software stack & OS in the Model S can already handle it. It all boils down to whether "the suits" at Tesla decide to block it or not. Based on what I've seen in the Roadster -- I wouldn't get your hopes up.
example: Tesla decided to cripple the Roadster cruise control and not let it operate below 35mph. The programmers had to go out of there way to put that limitation in.
example: Tesla won't let you look at the tire pressure figures unless the parking brake is engaged.
Dumb stuff like that. Kinda like how GM, Ford, Chrysler, Lexus all cripple their nav system when the vehicle is in motion even though there is no law regulating that. BMW, Acura, and Mercedes have no such limitation. It's just a case of super paranoid attorneys ruining it for everyone. Let's hope that a progressive company like Tesla doesn't succumb to overly conservative legal counsel and end up dumbing down an otherwise wonderful car.