It seems to me that creating communities, splits StackExchange quite a lot, and makes them difficult to start too.
Would it not be better to allow all questions to be in one big pool, and then have communities be views on the pool, with special review rules organised by that community? Posts sent from that community could automatically get a community tag, which would also make them beholden to the rules of that community.
Then communities that found that they had questions that spanned many different communities could point to those questions as proofs that there is an interest there, when arguing for a new community. Entering a community would not split questions apart from the rest, but be entry point for people from different domains to filter what interests them, allowing them to link to overviews of stack exchange that is easy to grasp for their members.
Just wondering if this process could be more flexible...