> Share the file system that stores media and documents
This is what the cloud is for. You're now going to tell me that you don't like that and would prefer local-only storage, but it seems like the vast majority of home and corporate users prefer otherwise.
> Use the same cpu/ram/gpu for both.
.. attached to your display and keyboard by a single USB-C connector. Or I suppose Miracast.
This turns into "would you like to buy a surprisingly not-cheap dock that's useless without the phone, or a separate computer that's properly adapted for its use case". Like 3D movies, it's something that the industry periodically comes up with, pushes for a while, and nobody actually wants because the compromises are too much of a downside.
It's far more likely that "smart home" and "smart TV" stuff will, very slowly, converge into a single integrated ecosystem where you can easily use your phone to control Netflix on the TV. "Casting" (a la chromecast) shows the way forwards.
