The DR1000S has some proprietary components in its reading system, but it does allow 3rd-party Linux apps to run and also to interface via is SDK. If the DR800 (
Mainstream iRex 8.1-inch reader for 400$) uses the same O/S and SDK, which I assume it will, then that will greatly expand the user-base and, hopefully, the developer base.
The only completely open-source option I am aware of is Open InkPot, which has its own forum here. It runs on the Hanlin V3, as a replacement for the standard firmware, and will also be the pre-installed firmware on the Azbooka 516. There are no 3rd party aps for this device, in part because most existing apps require a pointing device to function. The DR1000S's pointing device is its touch screen. The Azbooka 518 will have a touch screen and might be a good target for further open-source development.