I am not sure if that is what you meant, but some proper api documentation would be wonderful!
By this I mean commenting the code and then generating documentation from the comments, e.g. using Epydoc or Sphinx.
Indeed the code is not super huge and complicated, but having a page with a good overview is valuable.

I would be interested in contributing to such a project too. Also have experience with Inkscape and Python.

In addition to now commenting the modules you listed, it would be useful to have commenting guidelines for future extension developers.
Other work would be picking one generator, integrating it into the build process, etc.