The two examples you gave are close, but do not actually show what I need, this link is more like what I mean.
But, they did make me realize that the desired hierarchy can be achieved with a combination of css and selecting the right category/forum/topic order, and that the existing three levels (categories/forums/topics) is one too little.
This is what I think is a solution.
1.Create/give parent Categories a name to display as title in a new category header, remove all other data through css from the header, like the “topics” and “freshness” text since this needs to be echoed only in the next level of categories.
2.Create categories in parent category and change functions and css so they show as a list under each other and include topics and hierarchy text.
3.create another level of categories to act as main forums, here we include the freshness-links and topic count.
4.Topics/threads are created inside the fourth level.
5.remove the original bb-header to allow the first level categories to take over this function.
I think this makes sense to me, will have to try tomorrow if this works.
I can not yet make my solution of the freshness-topic-title public since I am working on a theme with this function included, I can not send private messages on the bbpress forum else I would have pm’ed you it as appreciation for your reply.
You can send me a mail and I will send you the code but please keep it to yourself.
seedism@gmail.com
Here is a link to a live demo, this is a work in progress and site is not close to finished but you can get an idea of what I did.
http://cultivators-forum.com/cultivation-forum/
Peter Hamilton