No one has implemented avoidance. It would be pretty trivial to do, but hard to support across numerous configs.
Have at it if you feel up to it.
Writing the code to run the obstacle avoidance is somewhat trivial, the problem I am having is incorporating it with the Mission Planner firmware, without having to type all of our own parameters in the thousands of lines of source code, which the current firmware does for us. If you could answer that for me, I would gladly upload a code for obstacle avoidance using four SRF04 sonar sensors.