Naw--just needs to be big enough for a commonly sized tablet (say 7" or 10") and then maybe a standardized (based on USB perhaps) mount system. I imagine something like an adapter plate (ala Apple's mounting plates) that provides both a customized mount and port adapting. You would just shove the phone or tablet into the mouth, port-first and let it click into place... then press an ejecting button to pop it back out safely. Just one example.

Why? Especially if the device can easily (and should) be removed when you're not in the car? It's not like you would stuff your phone/tablet in the glove compartment like people commonly do with GPS navigation devices.