> You nailed it with the GPU question. Think of real-time 3D graphics processing
> on board, while networked, etc. Choices of GPU hardware are limited, but they
> are there to purchase for mobile systems (laptop-like). "Embedding" drivers on
> a custom distro may be my biggest problem.

You might want to look at imx7 and depending on your time scale,
imx8. imx7 recently got mainline support for the GPU. It is often used
in automotive applications, and in-flight entertainment systems.
Mainline kernel support for it is good, so you can avoid all the
problems of a vendor kernel.