I think one of the most common requests and most common things I do is to extend the generic content module. It would be great if you could start with that, I'd even take the templates without any documentation.
I'm really surprised to hear that you had to refactor code to allow for these base modules to be extended. How was that not built in from day one? If you look at SF3.x forums, customizing modules is extremely common!
Looking forward to being able to understand how to build and integrate completely custom modules. Other than the missing functionality, this is a major hurdle for me t be able to migrate my 3.x sites to SF4.