Ifis a go then it is now critical to document the router. There is zero documentation as far as I am concerned, the rough overview over at Symfony is inadequate even for them and doesn't cover Drupal at all. We need flowcharts, internals (so that one can debug it), explanations (why do we use _controller / _form instead of just form? etc) and examples.
For posterity, the documentation or some semblance of it now can be found at https://drupal.org/node/2122071 . It didn't even take a year to get some documentation up. And that, of course, was not written by anyone in the WSCCI team because they are exempt from such small details like producing developer friendly, performant, documented code.