> google docs for chat is pretty ad hoc, which is fine at some level, but points to something (secrecy? ban-proof-ness? teenagers co-opting something where there might be a better solution, like irc or riot or various group chats?)

Google Docs for chat is no different than Wikipedia for discussion. The "Talk:" pages are group owned and visible to everyone. Google Docs has a realtime element, but otherwise works as a realtime wiki.

Plenty of internet discussion took place on the Wikis of old, not just Wikipedia but the original c2 WikiWikiWeb.

> How much is this discussion about centralization versus public versus private-facing communication?

This is tangential. People don't visit "vBulletin", they visit SomethingAwful. If you have a decentralized protocol (like vBulletin, PhpBB, Masteodon, or whatever), the laypeople generally don't care about that technological detail.

The typical web-user will be visiting "SomethingAwful", or "Digg". The webpage itself is associated with a community: a set of moderators.

Wikipedia and Wikia use similar software, but their communities are completely different. Federalized vs Centralized is a blip in the radar, its about policy, contributors and community.