I'm looking at simplifying the forum structure anyway - so we'll see where that goes - it's a trade off between having specific sub-forums for topics with lower posting or bigger generic forums with higher volume of posts.
I think that one way to go could be to put the "New posts" / timeline on top of the first page of the forum, maybe even on DB front page to lure visitors to the forum, it could also be made a bit longer, say 10-15 rows. That way guests as well as registered members don't have to navigate deeper to get involved, and people that visit for one thing might become interested in some random discussion.
If you have to navigate to find the stuff you're looking for you're excluding yourself at the same time from things you didn't know you wanted to know more about.