I have something like that running in my car now. Shutdown timer is important of course, plus a heartbeat. VGA or amp turn on delay is good. Standby timer, which wakes the PC back up after a given number of minutes/hours with which input woke it (or timeout so it goes to hibernate). ACC signals the software to shutdown and can and can be set to start the timer but I don't like that. Feel free to look at my code on my
car pc page.
After doing this, I think a PC controlled SDC is a very usefull addition.