It’s a little bit off-topic, and I don’t want to deviate the conversation, but I’d like to add my simple appreciation.
I think we are in an internet era where one needs to think about SEO or their users.
And I have no doubt that self-hosted Discourse will be used by those who choose their users.
I was looking for this feature because I have personal projects with the same audience and target. Multisite with SSO was the closest but I ending nowhere because it’s slow and not convenient.
I support the OP idea and start to follow this 