^your avatar suggest you might know some things we don't
As for the thought of doing it with arduino controls.....I like the idea...but execution is going to be a *!***. Can the arduino board support the voltage needed to run a door solenoid?
It wouldn't be hard to make a simple interface for on the tablet, you could probably keep it to a few "radio buttons" and regular toggles. I'd think the issue would be a failsafe. Almost every system would need a backup system, so you don't end up locked out of a car you can't even jumpstart.
Bonus if you can include air suspension controls.