I mentioned this on the form, but when you get to the second round group buy, please consider the following on top of ISO support if you don't already have them:
1) Support for a split backspace (relatively common on 60% boards)
2) Support for a split right-shift key with the 1U on the left. GH60, DZ60, and various other boards support this.
3) Support for a "minila" style split space key. On the original minila this is split in three with sizes 1.25, 3, 1.25. Support for this is very rare; the only PCB I'm aware of that has it is the GH60 (the DZ60 doesn't
)
This would be enough to offer full support for JIS layouts with keys either side of the space bar for switching between English and Japanese, which would be just awesome in a bluetooth keyboard -- I am not aware of another bluetooth PCB that offers this. Those keys can also be useful as function keys even if you don't use JIS; see the ANSI Filco Minila for an example of them in use.
I know this may be out of scope for what you are considering but I just wanted to point it out as if you were going to add these things doing it at the same time as ISO would make a lot of sense. We JIS users are starved of usable PCBs