Happy to read that! At last, you have your Surface fully operative.
In my case, I tried to restore from 0 using the image downloaded from Micro$oft and it doesn't work. I don't remember if I tried to format the hard disc, but Install from USB image, and after that I tested keyboard on every update (as image was a old version of Windows 10), but still doesn't work.
I am not sure, but probably doing a rollback doesn't "downgrade" firmware, only drivers. And maybe I2C devices could stay unreachable by S.O.
I understand that this things could happen, but the response of M$ is unacceptable.
Ruben