A nice 12 volt touchscreen with an Xbox resolution (720x480/576 480p 720p 1080i) and USB mouse emulation would work I guess, why not? Just need to invest enough $ in it
But for anything more then XBMC/Xbox games I would go for a non-Xbox solution. Cause c'mon, by the time you are done coding a new USB stack + dozens of drivers + navigation app for native Xbox we will all have flying cars and PS3's.
If you use something like a tablet PC with Windows, you:
- already have a touchscreen
- already have drivers
- can do video / audio
- can attach a wireless gamepad and run games / emulators
- can attach a USB GPS and run some excellent navigation programs with spoken directions etc.
- can attach a second monitor for the backseats
- can attach a USB DVD drive and mount it anywhere
- use a standard laptop 12V adaptor that won't drain much power
- use dozens of webcams for cool stuff©
- probably already have built-in WiFi
- attach a cell phone to arrange your calls / show who's calling / surf the internet with GPRS,UMTS,HSPDA
- send through GPS / webcam (driver's face!) data when your car is stolen (security code isn't typed within 1 minute)
And all you have to do is write a simple GUI to tie it all together