I had some time working on the subject.
I have tried to go on integrating a tether in Flightgear, but did not succeed.
At least there is now a github project. I can add anybody with a github account.
Otherwise, I have tried to order an openpilot Revo board, but we can not from France.
So I went on working with different parts (arduino + telemetry kit +mavlink + MPU9150 IMU sensor + Sabertooth motor controller).