I have the solution: Build more castle and less of other themes
In all seriousness, adding a General Mocs forum would be against the original idea of Classic-Castle. We do not need another mocs subforum to distract from the Castle mocs forum.
Even though there are age requirements at a certain general forum website, quite a few members are obviously underage there. I would suggest posting mocs on the appropriate theme website if possible. You should be able to post on Classic-Space, FBTB.net, etc. Comments on Flickr groups are also an excellent way to get moc feedback. There are multiple possible solutions to your problem which do not involve turning CC into EB or Lurknet.