The other side of the coin is the fact you can go directly to a Category your interested in instead of
multiple repeated mouse clicks to get back into "Challenges" for instance.
Breaking individual forum segments down into "trees" doesn't work, for this reason. Pretty much all you are guaranteeing are lots of dead sub-forums.
I don't really see the problem here. Maybe some general headers would be an advantage, but I have no major issues with the forums as is. If you are worried about missing a post, just hit "view new posts", and they are all there.
And if you post in the wrong section, a mod can move it.
Since it started on teh TS 6.6 subject, Most of the commets in that link are technical related, why not make it a sub category under technical help to get it off the main screen, and then additional subcatergories like the tutorial section, That way if someone has a technical question on VRAY and it is in the VRAY section, I know I can not help since, I have no experience with VRAY.
I think you have completely missed the point of the reason the 6.6 forum was created, which was to get truespace chatter away from other forums where users are looking forward (although imo most of the apps discussed are often more of a sideways move - you see the issue

), while giving grognards like myself a place to discuss truespace without having to engage in app wars. And while many threads in the 6.6 forum have been tech related so far, it won't always be that way.
Moving forums away from the main page is death, especially for a smaller site. Unfortunately, what may work for a technical document unfortunately isn't always good for community building imo.
This my pov, anyway.