Why would it be bad for another clan to be made? Because the others are lacking in members? There's a way to fix that.
And why can't there be a basic theme.. it doesn't really make sense. It's just something that'd be a little more talked about. If it really isn't allowed that a some sort of basis could be put in it'll be removed and turned into a normal, generic clan.
Cosa has started to flop because everyone is so different and there's very little common ground, or that's how I see it. So wouldn't have a bunch of people who like even a bit the same things be better than having a clan full of people very diverse in interests?