Perhaps there will be a G2 car dock but the op was asking about the G1. It is less likely that there will bea dock for that device.
Yes there are even less accessories for the G1 than the G2 at this point, though many of the accessories created for the G2, will work with the G1. But if I was a betting man, I wouldn't bet on a dock for the G1's at this point.
If you were to pause the player and you had a switched accessory that turns off with the key, the player will turn off - and then on again with power. But only if you pause it (or unplug the cable from the headphone jack which pauses it) before turning the key, and only if you have the option of a switched accessory. Even then it will wait 30 seconds or so for no activity and then shut off but it will still shut off.
Interesting I know on the G2 that when you remove the headphone jack it doesn't go into pause automatically, so that apparently that was removed. But this is good for the G1 and since that is what the OP was talking about. However, I understand that if you manually pause the G1 or G2 they will both shut off after so many minutes or at least go into standby, then after another period of non use they will both actually do a hard shut off. I know my G2 will power back on so I assume the G1 will too, but it will remain in the paused state until you manually reach over and push play and this has to be done within a couple of minutes are it will go into standby.
However, I got the impression that the OP just didn't want to have to do anything, but turn the ignition off and back on. But he would have to pause and/or unpause. But after thinking about it, your post would indicate this would be doable if he was leaving it in his car as he says. Me, I wouldn't be leaving mine in my vehicle. But if you were taking it out, that would mean you'd have to insert the power and headphone plug. I am doing that now myself and it does get old, but until there is a dock I have no choice. Though as I said I doubt they will ever have a dock for the G1's, but those of us with the G2's may luck out eventually.
I only learned about the "pausing when you pull the headphones out" thing recently. I always throw it in my jacket wherever I go, so now I just unplug it from my line-in (I only use USB power on long trips in the car) throw it in my pocket and don't worry about it. It shuts itself off.
Yeah too bad the G2 doesn't support this! Though it will turn off if you manually pause it.
Look closer DAB - there is a door (you can pry it with a fingernail) - there's actually a small hole you're supposed to use an open paperclip in to help open it. It actually has a (rather fancy) spring-loaded mechanism to hold the door on. The trick to opening it without a paperclip is to get nails under both corners of the door and pull evenly.
Yeah, I was thinking G2 and not G1, but you know there are those that say you can't buy batteries for these things? I have never looked because I currently only have the G2 at least until my woot arrives.
I do have concerns about my headphone jack because inserting the plug in that jack so many times will surely wear it out. So a dock would resolve that!