For the next version of APM (the fixed-wing codebase), we're thinking about adding an acrobatic scripting language, so you can program your UAV to do awesome robotic stunts. APM already suppports inverted flight, and adding other maneuvers is technically easy once we decide on how to program them.
As a comparison, the UAVDevBoard uses LOGO as its scripting language and also supports inverted flight and harrier/hovering. APM does its scripting with MAVLink via the Mission Planner or HK-GCS, which is a more visual way to plan a mission.
One option is that we could add MAVLink commands that took the following form: