I just discovered the newish capability of RTL flying to the nearest Rally Point and the Moving Base capability of Mission Planner. Its my understanding that RTL will fly to the nearest Rally Point. If Rally Point 0’s position is changing while the copter is in RTL, will the RTL landing algorithm continue to monitor the Rally Point location? In other words, if you are on a moving boat, would RTL land at the current boat location (assuming the GPS position is accurate enough)?
From reading the control_rtl.cpp code, I would say no.
The path to return home is computed only once when you flip the RTL switch.
However you could do a custom mode fusing the Follow Me mode (http://ardupilot.org/copter/docs/ac2_followme.html) so your drone come back to a moving GCS and the precision landing stategy (for landing on a moving target) .