[follower]

> My best guess is that it was something of a gimmick for Google I/O. They never seemed well-supported by Google.

I would agree. I created the Handbag for Android project (http://handbagdevices.com/) which was initially based on the ADK so I've spent a lot of time with it. In the ADK 2.0 release Google itself even moved away from having the physical USB link in favour of using Bluetooth.

When 2.0 was released I started converting Handbag to have the option of Bluetooth/WiFi/USB but the ADK stuff was so unreliable (and the debugging was ridiculous due to different issues on each Android version available at the time (2.x/3.x/4.x)) that it seemed like a waste of time to continue.

The goal of Handbag was to enable an Arduino sketch to create an Android UI and have bi-directional communication between the two devices. It could be interesting to adapt that aspect to run with the linked project.