Mini-update: I assembled one this evening and it works nicely. Looks like it will even fit in my aluminium case with about 1mm to spare vertically
Here it is: top layer is LCD (and a little riser for the rotary encoder), middle layer is the custom PCB, bottom layer is Arduino.
Website will be updated on the weekend to have the design files and assembly photographs. The rotary encoder has a push-switch action (all wired in through the PCB) that the source doesn't support properly yet, it's connected in parallel with the foot-switch; I'll have to make a bit of an update over the next couple of weeks to incorporate that nicely instead of the current approach where keypad-# is the exposure button.
Definitely taking orders for PCBs now; the question is whether people would like basic parts kits of the annoying-to-find things (encoder and pin headers) that are hard to buy in single quantities. That will make shipping more expensive though since it'd no longer be a "letter" under 5mm thick.