Just a little update to let you all know this project has not been abandoned yet :).
I have made some improvements to the feathering code to prevent it from overlapping itself so easily. Even though it now works better than before, it still isn't as robust as having a second bézier shape (like in Nuke). So, I've decided to add a bézier feathering mode to give the user the option of using it when the current method fails.
I have also started working on a dedicated Roto2D compositing node. At the moment Roto2D uses a standard Image node which is less than ideal. The new node will fix the current rendering and undo issues. The next release will probably be a intermediate one with parts of the script moved to the node but not all of it yet. I'm still working on the best way to allow the node and the image editor to interact and right now python gives me a faster turn around.