I was surprised to see we have separate communities for bitcoin, ethereum and perhaps other individual cryptocurrencies, and no overarching cryptocurrency site (we have cryptography but not quite the same) If we take SO as an analogy isn't that like having separate C++, C#, Java, JS communities? And SO is huge but I don't see proposals to split it up.
It's just one example but I have no idea how or indeed where one might suggest this sort of thing. Do individual communities have full control so they would have to agree to merge or does SE have control over this sort of thing?
Hypothetically, what would be the way this happens in the SE ecosystem? Create a new community which subsumes several existing ones and see if the old ones wither with people migrating seems pragmatic but somewhat cynical.