I would like to go something like "batteries included but not installed." The User interface I have now is a good example of what I mean -- I would prefer to keep everything built around implementing an interface, but it might be nice to provide an "official" authentication implementation as a subpackage.

I've started writing subpackages as they become important to me. The most useful thus far is probably gadget/forms, which is very much inspired by Django forms. I prefer a data validation layer that is independent from or at least very loosely coupled to a model layer.