If you can see it, it can key it.
The same goes for any keyer though
The question is how far it can really make that happen, it's not like you couldn't seperate chroma and luma for a key manually. After all, I've yet to see a tool that works as good and perfect as advertised in the shiny demo papers and videos.
I don't want to say this keyer is not appreciated or so, but at the current state Natron needs other things more than that. Further, it's not like you could just "make" it that easy, it's not like Disney Research did not invest a ton of money to develop that. I mean you made the INK, you know much more about programming than I do. Any company that would pick up that paper and build a usable Disney-Keyer could make a killing!