I don't know that ChromeOS uses X server (I know almost nothing about it, in fact). But by the time you've paid for the additional hardware, it may be the case that it's cheaper to buy a tablet or a professional-grade IDS display.
ChromeOS doesn't use X11 any more. It uses a custom graphics stack called Ozone[1] that runs on top of libDRM on Linux and uses features such as hardware overlays which are common now that X11 knows nothing about.