thank you very much to the anonymous person who pointed me at a *FULL* Rockchip RK3399 Reference Design including Technical Reference Manuals, full schematic file and full PCB CAD design files.
using that design it will be possible to create an amazing CPU Card... unfortunately running MALI.
http://rockchip.wikidot.com/rk3399
this shows that it has USB3 however it does not have RGB/TTL, so it will be necessary to do a conversion from MIPI to RGB/TTL with an SSD2828 or similar.
the Reference Design has twin 32-bit-wide LPDDR3 ICs so there is the possibility of getting not just decent performance but also low power at the same time.
l.