Sorry that it's not an answer to your question, but I think its important to see what's out there.
hasn't been updated since 2007
Kytten
Development has stopped
Themes are a pain in the ass and the default look is pretty horrid.
The code is nice though so could probably be forked quite easily.
SimpleUI
Hasn't been updated since 2009
although the developer is still active here
Pyglons
Seems to have its own (its based on pyglet)
Not sure how complete it is.
PyChan
Used by FIFE (recreating the fallout engine)
But it's bound to PyGame (SDL+PyOpenGL).
Would be interesting to see if it could be decoupled.
Unfortunately it's XML infested
PyMT (multi-touch)
Became Kivy, so I guess it's not actively developed.
I dislike Kivy, but that's a personal opinion.
These are all projects that try and invent their own UI system.
This is fine for small projects, but larger projects should aim for a more robust UI tool such as using existing HTML / CSS renderers.
Berkelium
Free binding to Chromium, unlike non-free awesomium
Would be a good choice for creation of some bindings.
Kivy has bindings here:
Haven't taken a look, be good if the 'Kivy'ness could be stripped out.
Librocket
Uses HTML / CSS for rendering UIs.
Unfortunately it is for C++ projects, it's 'python bindings' are actually just for writing scripting logic inside the UI, but it doesn't let you use it from a python project.
Took me a long time to figure that out.
Cheers,
Adam