A topic I see come up quite often is how to change hibernation screens, going into and coming out of. And there doesn't seem to be an easy answer.
How about doing away with it altogether? Would there be a way of sending a VGA signal from another device inline with the VGA lead to display a "Please wait...." screen or similar for a determined period of time? Until the PC is up and runing. Then allow normal VGA through? And the same for shutting down.
Using a trigger from the ignition to tell the unit to turn off, and a trigger from the PC powersupply to turn on.
Just an idea.