guys it's pointless to debate about HHKB compatibility, as disappointing as it could be, that ain't gonna happen.
Once your colors/font are decided, should launch an IC poll "Are you interested in purchasing this custom Topre keycap set?" with options
"Yes, I will purchase this set as it stands (107 key)"
"No, I will only purchase this set if it also includes HHKB compatibility caps"
"No, I will only purchase this set if it also includes FC660C compatibility caps"
"No, I will not purchase this set"
then post a link to it here, reddit, DT, EnjoyClick, KBDMania, etc. If we can show Topre how much money they'll miss out on by not increasing their manufacturing cost by <5%, might be able to change their mind.