When single user interfaces start becoming problematic, they will be. Neither of these platforms have reached a large enough size to need it, but it will eventually be necessary for groups of servers to only federated with themselves to ensure compatibility and scalability. We already have issues with propagating content, systemic and programmaticly.
Sure, but the users cost is what really matters, and that’s down by many magnitudes. It’s fractions of a penny for me to send millions of words a second across the planet.