Oh yeah lots of people do similar stuff, just check any sport compact tuning show site for lots of ideas. Clarion, Pioneer and Alpine, to name a few, make dash-mounted retractable touch-sensitive LCD displays with built-in DVD head units. You can easily connect a laptop via RCA to that system, and by extension to your car's sound system. Most of these display systems also have connectors for navigational systems and GPS trackers and stuff. Mind you, they're all pretty darn pricey.
But the ramafications of installing a keyboard in your car are more than some might think at first. A car stereo interface is designed to be simple and easy to use when you're not looking at it for safety, it's not as easy to navigate your iTunes music library while you're driving