I think it should be left as is. A Warbird is a Warbiird. When you start to split a forum into smaller groups, it gets harder to find or disperse general info, that will fit more than one group of warbirds.
As an example, if you have a question about a B-24 model, should you go to the Warbird forum, the Twin Forum, or the Scale forum. What happens if it gets split up more. I think the set-up we have now is a good one.
On the other hand, if it does get split-up, I will still read all the related forums.