I saw the HUD on the most recent BMWs and though it seems like a cool piece of technology, I am not sure if it's something that I miss sorely. Don't get me wrong, I was definitely wow'd when I saw it but in the end the amount of information that can be displayed without distracting the driver is limited. I am sure someone can prove me wrong but I have not come across it, not yet.

Given the amount of used cars that are sold every year, and the way people get wow'd by such technology, I would say it's worthwhile to build a SDK and at the same time provide an example of how to make a DIY HUD, if you get a lot of traction you can always make custom HUDs that users can buy directly from you (kickstarter project).