I'm actually working on some new auto mission code myself. (You can find some discussion on it in IRC logs.)
I've been busy with other stuff for over a day, but this weekend I plan to get a substantial amount of work getting it closer to completion, if not all the way. (Friday for me is mostly tied up.)
The new system will eventually be rather sophisticated and handle nearly any mission (including base defense, downed pilot rescue, and others), but to be honest I can't promise it will all be fully implemented in 2.4. What I'll probably do is cut some corners here and there, leaving some fancy stuff out, for 2.4, and after 2.4 gets out the door I can develop it further, down the road. A priority I'm making is to get a simple implementation of it working, get the bugs worked out, and then later fine-tune and add stuff.