This is how Threads would take over the Fediverse and eventually win when they decide ActivityPub development is too slow and holds them back.
Boom all your communities are now empty.
Federation works because we’re spread out. Just subscribe to all the small communities.
Now, what might be a better idea is a cross post functionality where the crosspost has a single identifier of its own so it only will show up once in your feed (I guess as your local instance)
That way you can have the ability to reach everyone as if you had posted a bunch of times, but a big popular corporate instance can’t gather up all the communities and then defederate and wall them off.