I am working on a dev branch for scientific purposes - with ROS (Robot Operating System) integration both on the flight side and on the ground side.
The idea is that you can use HITL/SITIL with the GCS to link to ROS - for example for ROS based vehicle simulators (the additional level of abstraction would allow to link with a vast number of simulation toolkits that already have ROS support) but you can also use ROS on the vehicle. This is done by connecting the flight controller via USB to a "main computer" - it then uses the VCP (virtual com port) to exchange data with ROS - exporting state estimate and receiving waypoints for autonomous navigation.
I have the dev branch for that on
https://github.com/robot-perception-group/LibrePilot but I will need some help to get that back-integrated into the main LibrePilot code.