The USB thingy already exists, I actually own one for macros with dumb keyboards. Its a very small USB-device with a USB port where you can attach standard USB keyboards. It runs QMK and essentially acts as a proxy, allowing you to program macros and what-not directly in QMK. A neat, little gadget.
See https://geekhack.org/index.php?topic=69169.0
Edit: Correction: It actually runs TMK, but I flashed QMK on it.
Re:New 13-inch MacBook Pro
by geoelectric on Tuesday May 05, 2020 @03:05PM
(#23083579)
Sweet! Thanks for pointing me at that. I have applications where I might be able to use that anyway (PS4 comes to mind).
As far as the immediate concern goes, Karabiner is such a popular thing that I suspect there'll be some way to support it. If not, I won't upgrade. I just bought this MacBook Pro, and it'll probably continue to be usable on 10.15.x for its lifetime. I'm not too interested in my gaming keyboard and 10 key pad becoming unusable, at any rate.
If they actually completely kill software support for this, I guess next best thing would be a USB intermediary to process the key codes. Possible it's doable with a Raspberry PI or something, and there are enough mechanical keyboard enthusiasts on Mac someone would be motivated to do it. Won't help for the internal keyboard though.