LegioXV, not it's not supported in Starling and GM runtimes yet (the latter is maintained by YoYoGames who'd need to add this functionality.
famusrock, that's awesome! Batching is much easier to retain with software clipping than with stencil. The latter, as you identified, introduces a lot of complications, and making it work with arbitrary rendering graphs without breaking batching is extremely hard. I'll try to figure out the best clipping algorithm for our use case. Since we only clip triangles against arbitrary polygons, there may be some tricks we can apply.
I should also note that no matter how we implement clipping, it will always incur runtime overhead. Nobody should apply it to all their skeletons in their scene, we will not be able to make it work fast enough in that case.