I'm restarting work on this. There have been plenty of implementations of this already, and the protocol is seemingly simple to bitbang. In fact, most implementations of this are essetntially bitbanging at the right speeds to perform the magic things.

There's an arduino with USB host capability that I'm in the process of acquiring. I've just moved and settled in and finally moved my computer stuff into its permanent home, so forgive me for taking so long on this.

Essentially, there's an USB stack for the arduino that allows for controlling a keyboard and mouse. The other end would just bitbang everything to a ADB keyboard and mouse.

I've already had limited success with speaking ADB via an arduino and there's plenty of reverse implementations of this on the internet.

Everything will be opensourced, and should be possible via an arduino.