You could have a standard for a board connection, or even produce a cutting list and engineering drawing. I was thinking about this earlier on, what if double skin ply is used. Perhaps a consensus can be reached. Or perhaps even a "Converter board" Two skin ply would probably be my preference, due to weight considerations. No reason you couldn't have a solid piece at the end to allow for a g-clamp.
I have decided to have a go at making a Freemo module. I just need to gather to wood and things ready, then when some definitive ideas come out i can get cracking. My main considerations are this:
Board joins
Wiring
Connecting electrically to the next board (although crocodile clips would work, maybe have bullet connectors or something).
You could fit a switch underneath to allow for going between DC/DCC operation, depending on what it's used for 'at home'.