Well, the one thing that would be different is that backend-Twitter has an incentive to keep all the baby-Twitters interoperable, so we kind of get federation f

Well, the one thing that would be different is that backend-Twitter has an incentive to keep all the baby-Twitters interoperable, so we kind of get federation for free, via an unlikely route. Yes, we have federated services now, but the largest and most popular services are non-federated walled gardens.