I'll be the odd one out and say I support this model but for other reasons than the technical limitations and scaling problems involved. For me it's more about trying to establish a tighter ring of trust and enable easier user onboarding as the hub could serve as the primary identity store for users on multiple instances.

I mentioned it in some chat earlier, but I think that the Beehaw.org moderation model, goals, and philiosophy serves as an excellent starting point for like-minded communities to build out the hub-and-spoke. It would also give them greater flexibility in maintaining the health of their corner of the fediverse by centralizing identity with them.

This model would, of course, not stop others from creating their own hub and spoke and would break apart the fediverse a bit, so I suppose there should be a way for "hubs" to talk to eachother in a way that resembles what we have now.

From a blocking bad actors standpoint (I'm still upset about Captcha getting removed even if it's a technically inferior solution), it would be far easier to have fewer hubs to need to blacklist/whitelist than having to do it for each individual instance.

I guess to go a bit further, if Lemmy could support both "modes" (as in it can be configured to be hub and spoke as either the hub or spoke, as well as retain the existing functionality for those who don't want a hub) that would be ideal.