It seems that you're already working on this - I just stumbled across this in the CE specification:
In addition, for this community, CircuitCo Inc. plans to make available an initial low cost
maker mezzanine board that will provide the following functionality:
● I/O level shifters to 3.3V/5V
● 0.1” header for easy access to low speed expansion I/O at 3.3/5V levels
● Raspberry Pi compatible CSI camera FFC connector
● Arduino Uno compatible shield interface
● Standard UART connector interface
This board will connect to any 96Boards CE compliant board.
Is there a rough estimate of when the mezzanine board will be available?