You should put up an informational website to let people know, at https://info.info/

Do you otherwise have no spare pins? Also you can do communication between halves with only a single pin, what protocol are you using?

The other thought is, does the LCD use i2c and are you using i2c between halves too? If so, does the LCD modules have a way to change their i2c address so they don't conflict? If so you should theoretically be able to have all of it share the same bus (the same 2 pins).

Even better would be to use git submodules for them rather than copying the into your tree.

if you can stomach the low key count I'd highly recommend something like the Sweep. if built wireless it becomes an even better travel board IMO but it's not a necessity. Also sometimes uni-bodies can make good travel boards as they work pretty nicely on your lap or other awkward situations a little better than a split. Personally I have an Osprette which I love.

The others you've listed are all good options too. Good luck.