I really like my keyboards wireless, specifically BLE (so no receiver dongles).

I also like them to have long battery life (months).

I don't care for backlight LEDs.

Is there existing open-source firmware that would tick these boxes? I couldn't find anything last time I looked.

(I own and love an HHKB Hybrid Type-S, but am curious to what extent it can be replicated -- and then tweaked -- using open-source designs that already exist.)