I have just stumbled upon this year-old proposal on https://deskthority.net/workshop-f7/hid-io-sideband-input-device-protocol-spec-t12927.html, which I think is extremely relevant for keyboardio.
In short, it’s about a side-channel extension to the current HID protocol for keyboards, that would allow sending arbitrary unicode characters to the host, as well as other goodies such as on-screen display of the actual layout on your keyboard.
I know of two small companies interested in this proposal (Input Club and Kiibohd). What I know was surmised from this issue on Kiibohd github: https://github.com/kiibohd/KiiConf/issues/30.
Now, the road ahead is long and winding, but I hope that by joining efforts, it may be possible to push this proposal to the appropriate USB committee.
I hope this has sparked some interest!