I figured the changelog was more a hedge vs bad actors, e.g., someone who says a bunch of stuff including controversial statement c and then edits it out later. I don't imagine that, in practice, people would use the changelog for anything real, just like they don't on Wikipedia.

Actually, the Wikipedia model is kind of the right vibe. You can see how tortured this gets on Twitter, where accumulating knowledge about something can only happen in a thread, because Twitter doesn't support an abstraction that gets at the use case people are trying to express. Twitter doesn't care, bc it's not trying to be a place where real discussion can happen, or knowledge can grow.

Whether this is the right thing for SN or not is an open question. I think I would use it, and I think it would let interesting new forms of community emerge. But who can say for sure without trying it.