there has always been alot of interest in a double-DIN touchscreen monitor, but the options are very limited and the prices have been insane. one reason I think the prices always end up too high is that there are too many unnecessary features being added. it sounds like you want to make a product similar to the CT650A. that will be a nice product, but IMO the price is going to be too high. the selling price will ultimately determine it's success.
I think you should keep it as simple as possible in order to keep the price as low as possible. I don't think the USB HID features are necessary. personally, I would like to see a double-DIN chassis with pre-installed VGA touchscreen. no buttons are necessary on the front panel if it turns itself on/off automatically, and switched to rear-view camera input automatically (other buttons can be on the back, or via remote control).
don't even consider using anything less than VGA resolution/input. a carPC is useless without VGA, as text is not readable. also, there are plenty of non-VGA double-DIN monitors out there to choose from. the gap in the market is for double-DIN VGA monitors.