Admin to Create User type Foo that can then Create User type Bar
@cwiggo Drupal doesn't really have a concept of a user 'type', just roles that a user can participate in, which I presume you know. You can of course layer 'types' on top of the provided structures using additional fields and tables. You've obviously looked at some of the candidates for helping with this, but have you considered Organic Groups, which might be closer?

As for using projects before stable release: my best suggestion is to dive in and help get a project over the line, perhaps by contacting the module maintainers and offering to help directly. There are however a lot of sites based on 'dev' modules; the maintainers just have to evaluate the code, the issue queue, and the overall risks/benefits and make a decision.