Drupal 6 and future development of outline.module

Here is one piece of good news.
The book.module mega patch that pwolanin has been working on for months has been committed http://drupal.org/node/146425 .

This patch which implements much of the same functionality as outline.module will be part of Drupal 6.
Yet, it does not implement many of the functions I had in mind for outline.module.
The question now is: can we implement those functions with a contrib module that would depend on core book.module?

In any case, an upgrade path will be provided to whatever solution we chose.

In practical terms, it means that I won't be developing and adding features to the Drupal 5 version of this module, until we are clear about what the Drupal 6 version of outline.module would look like.

You can help this way: Please test the Drupal 6 book module. In many ways it is much better than the current outline.module (better javascript and better everything else...) Is there any feature missing in D6 book that exists in D5 outline?
Would some features be impossible to implement for D6 book that are easy or at least possible to implement with D5 outline?