Another question, this time mostly idle curiosity.
Almost all GPIO/I2C/SPI is routed directly from the RK3399 to the Edge fingers without level shifting. One exception is I2C8 which you level-shift from 1.8V to 3.3V before you bring it out on EF1 and the FPC connector.
Is there a reason for doing this - did you have a specific application in mind for I2C8?
Slightly surprising consequence is that of 11 IO lines on the FPC connector (and therefore the Edge IO), there are three different voltage conventions: 4 GPIO and an SPI at 1.8V, 2 GPIO at 3.0V and a dedicated I2C bus at 3.3V.