...it doesn't need to be a huge company (or company of any kind) to run these things. Back in the early 2000s, a volunteer who knew about computers would set up phpBB on a church's website, or a radio station would allow one IT person to spend half their time maintaining something like this, and that would be it. No need to turn millions in advertising dollars to have an online community.

I do agree with the parent comment, that we may well see a resurgence of small and medium-sized online communities, for the simple reason that more fragmentation could be a good thing. When a community has its eternal september, people can move elsewhere.