It seems like this might support a distributed capability model system.
Here's a good discussion on the differences between macaroons and capabilities: http://www.eros-os.org/pipermail/cap-talk/2014-December/0163... (see the "Macaroons: Capabilities vs Credentials).
This is very exciting stuff. Thank you for writing such a great article about it, I'm looking forward to reading more. And I have a copy of your pymacaroons source printed out to peruse. Cheers!