I have been spending some time on the #reprap IRC channel lately, and there seems to be some demand for an on-printer user interface. When I first heard this, I was ecstatic - my company once produced an aftermarket iPod interface for automotive use. This interface allowed the user to control their music with a four button + 16x2 LCD module. Now that most aftermarket head units come with iPod control built in, there is no demand for our product. As such, we have a large quantity of these modules and very little use for them.
After realizing this opportunity, I began testing a module to verify the protocol spec. After hours of beating my head against an invisible protocol wall, I realized my FDTI USB-serial cable wasn't providing enough current. I moved the power and ground lines to a 13.8V supply, and BAM, text!
Pending permission from my employer, I will release the protocol specification and device schematics.