We've had the great fortune (or misfortune, depending on your perspective) of having to build and install custom images on two different types of Android tablets in the past.
In both cases, it's taken direct communication with the manufacturer, a mishmash of proprietary tools that only run on specific platforms, and much labour.
As far as I know, there is no "standard" imaging process. The tools and techniques seem to vary significantly for each manufacturer, and are often difficult to obtain (for legal and copyright reasons).
We have an eclectic collection of documentation and tools from various corners of the Internet (xda-developers.com, stackoverflow, etc.), but have yet to put it all together into something that even resembles a reliable, repeatable process. Much of the information is old/outdated, or device-specific.
I fear without guidance, many (perhaps most) teams will simply not be able to submit their work due to the time, complexity, and overall obscurity of the task.
Worse yet, hundreds of person hours (have been / will be) duplicated and wasted on a mundane technical procedure that could have been spent on the actual education component.
The Google engineering team that created the Pixel C clearly have reliable tools and instructions at their disposal. The X-Prize technical team also seems familiar with the process.
Is there some sort of legal/licensing issue that is preventing the tools and information from being distributed?