-cough-
Eurobricks, then -cough-
The thing is, it's like you're being completely ignorant of history here. Back in the day there was one big all-themes community site, Lugnet (well, that's after alt.toys.lego and rec.toys.lego). CC was created because of a dissatisfaction with that model, and a desire to create a theme-specific site (as were other themed sites). As a result, we've seen much more growth in the castle theme, with innovative building and actually more conversation, than we had when it was one big conglomeration. I would also say the same about other themes as well. The reason we have a vibrant community here is because of this move to have a focus. The AFOL community as a whole is highly interlinked, with people being members across multiple forums, and general blogs like the BB to help point us all to cool stuff, not to mention Flickr and Brickshelf, also fests, so there is still a lot of cross-pollination between castlers and spacers and trainheads and mech guys and customizers and SW fans and pirates etc etc etc. We don't need to try to return to an all-inclusive model. We don't need to try and drag people away from the forums they normally frequent by trying to be all things.
Also, one of the problems back on lugnet was 'overcompartmentalized dorkism' - as there was a great variety of forums and sub-forums, there was always a lot of meta-conversation about what topics go where etc. At times there was more of this than actual conversation. Subdividing forums needlessly leads to this.
BTW, Richard, please feel free to post on any non-castle LEGO topic, including your MOCs, in the general LEGO forum. That is its purpose, as described in the FAQ etc. Perhaps a better tag in the Board Index page would help here. Instead of "Discussion of general LEGO topics", maybe we should say "MOCs and sets from all non-castle themes and general LEGO news", or something.
Bruce