I’m a little late to the party, but I just wanted to share some thoughts on the expansion board mentioned in the first post.
Rather than using a ribbon cable to connect a second unit, you could instead install some form of mezzanine connector on the underside of the board which would allow you to use the existing case as-is.
If the expansion board sat underneath the main board and was supplied with a case extension (Basically just a short tube of plastic that accepts both the original lid and base), upgrades could be performed by the user. (Open the case, connect the new board up, put the case extension in and stack it all together with longer screws.) This would mean that less surface area is used, no new mounting holes are required and all of the parts from the original unit (Except the shorter screws) are used reducing waste.