Regarding splitting the forums, I can understand the appeal, but the demand question is curious. Obviously there's interest expressed in this thread in it, so to say "there's no demand for this" is incorrect and, honestly, kind of insulting in a thread specifically inviting comments and suggestions.
Yet at the same time... I don't see the drowning-out effect some of y'all are mentioning here. From my view of the forum, it looks like we don't see Diplomacy-related threads on here because no one posts them, not because they get posted and then drowned out by the Diplomacy-unrelated threads.
On this particular front I tend to be more of the DIY school of thought: if you want to see more Diplomacy discussions, ask a question or post a premise about Diplomacy in a new thread on the forum, and it'll almost surely happen. When they're posted, these discussions tend to go pretty well in my experience. They just don't happen because no one really bothers. Again, obviously demand is being expressed in this thread, but outside of it I just haven't seen it.
Indeed the fact that the forum is predominantly unrelated to Diplomacy speaks more to me about the essential character of it; people just plain want to talk about things that aren't related to Diplomacy more than things that are. I think splitting the forum would just lead to one barren section with sparse discussions of Diplomacy and then another section essentially unchanged from what we have now. The issue seems more to be that Diplomacy isn't discussed than that it's crowded out, and while I can understand that point of view, there's just not much in the way of a top-down solution. We could ban non-Diplomacy discussion like other sites, but that would just kill the forum and thus a large part of the site overnight. We could split the forums but that won't affect the supply & demand of Diplomacy threads. Honestly I think the only solution is bottom-up, create more Diplomacy threads and the forum will feature more Diplomacy discussion. In that respect I'd be happy to help, I love a good Diplomacy discussion.