First one is terrain following using LIDAR or another sensor?
Is it possible to flight mission at fixed altitude above ground, even when ground is not flat?
I found some mentions about it on Github, but Im not able to found current status in documentation.
GitHub issues:
Second topic is compensation for magnetometer dependent on motors current. This feature is named in ArduCopter MotCalibration. Is somebody working on this field?
Terrain following with EKF2 should work nicely when https://github.com/PX4/Firmware/pull/4741 is in. You can use any supported distance sensor. (I closed the above issue because it was stale)