This is almost exactly what I’m after. Will probably pick one of these up and experiment with flashing it. The big assumption I feel like is that the keyboard just registers as a normal HID/USB device and will work with any os. Fingerprint and stuff could be fiddly, but we’ll see.
I have a Boox for when I want a bigger screen, and a Hisense touch (I think that’s the model). I like them both a lot. The Hisense device is also a HiFi audio player which is nice.