I think you are deliberately missing the point. CSH can be London's Folk Centre and a National centre at the same time. Why on earth not? What's the evidence that it's only used by Camden residents? And even if they were the majority users, surely it would be their ticket money subsidising the organisation's national role rather than the other way round?

I don't live in London so I haven't been to King's Place, but from its web site it appears to be a fairly pretentious glossy "arts" venue for the wealthy, judging by ticket prices. I couldn't see that it has a library housing nationally important folk song collections, for example, or the range of classes and workshops that CSH holds. Presumably your idea of what constitutes a folk centre is different to mine.