The problem with the CAP forum, as you've mentioned, is that it does not seem user-friendly and looking at the most recent threads one would think that the CAP forum is only for threads that pertain to the current project at hand. Very few threads pop up during the Policy Review stage between CAPs because the forum seems like a place for producing the CAPs, not discussing them.
About long threads: there's nothing wrong, in my opinion, with long threads. The problem is that the only threads in the forum are "CAP 2- X Submission", "CAP 2 Pre-Evo- Stat Poll 3", and "CAP 2- Art Discussion" and such. This makes it look like posts concerning general discussion, specific discussions, RMTs, and other threads don't belong in the forum. I don't think there is a quick fix for this, but the way to fix this is to gradually introduce more non-process threads into the forum to give it more of a feeling that, at least between CAPs, it's a forum for discussion first and a CAP factory second.
Projects like the Dark Horse and CCAT would be great ideas IMO, especially the latter. I don't see Dark Horse working here because there are no CAP stats to work off of and the new CAP metagame is still in its infancy. CCAT would be a good idea if it could take a shorter time. RMTs should also be a common occurrence here for the purpose of commenting and improving teams. The only RMTs here are showcases of great teams made by usually well known people. Another good idea would be the Counterteaming project done in UU where people make two teams and alternate in a 1-2-2-2-2-2-1 fashion in order to counter the other team. The two people who contributed the most get to battle each other with the two teams.
I would love to be involved with a Community-Create-a-Team or a Counterteaming thread. The Counter that Pokemon! thread that was in DST might not be the most intelligent form of getting discussion, but it could definitely "break the ice" per se and get more people posting causally in CAP.
One more thing: posts are super-long in the CAP forum because most threads are either related to making a Pokemon (and need to be long so they get slated) or policy threads (which are usually debate forums filled with long posts). If we change the atmosphere of the CAP forum, the tl;dr will follow.