That’s fair. Assuming people do behave that way, it wouldn’t be an issue.
On a slightly tangential angle: what about the communities that maybe won’t have a dedicated instance, like: corgi, cooking, jokes, etc… all those communities and posts would be on the biggest instance(s). If the devs don’t want this instance to be the flagship instance, once/if lemmy hits sudden growth they’ll be in for a rough time. :P
I just feel like this approach isn’t super conductive to decentralization. In the alternative scenario you’d be seeing corgi pics all over the network, this way most likely just here. But maybe that’s just an issue of lemmy’s current small size, and would be solved on its own once it grew, and the number of instances grew. Maybe I’m underestimating the growth potential of smaller instances.
I think you’re getting hung up on the word “federations” (noun) instead of the adjective “federated”.
Who decides who gets to email who? The email provider admins. Should everyone be in a single email network/bubble since otherwise there is no communication? Mostly, yes. Do I need a separate account per email bubble? Per email bubble? Yes. But how many email bubbles are there? One? Whats the practical limit on number of providers per the email world? None, mostly?
Gmail does ban a lot of small email providers if they don’t seem “legit” enough. And that is where you’re onto something with the noun federations.
If a bunch of instances really disliked a different bunch of instances they can indeed severe each other from each other. The admins would do that. They put the other instances on a block list. Most Mastodon instances block Trump’s Lie ehm Truth Social etc. But otherwise you can talk from gmail to hotmail to mcselfhost, with one account.
Basically federation works based on a block-list, not a allow-list, unless the admins of the instance set it that way, just like email providers.