Video not playable on rPI? People get your facts straight, rPi is very good at playing videos (1080p). It has a OpenGL GPU very capable but unfortunately there's no accelerated X Server driver for it. There is an ongoing effort to bring Weston Wayland (which emulates x server) accelerated to it though. I think there are tuts out there about how to get it running already.
FGS, have you seen how this little thing runs Quake 3?
The main problem with using this in a car is the GPS software choice. If it would run Waze and iGo i'd scrap my nexus 7 from my dash tomorrow.