I’m not saying everyone will run their own homeserver (setup/maintenance costs, maintenance skills required, and economies of scale combined guarantee some cons

I’m not saying everyone will run their own homeserver (setup/maintenance costs, maintenance skills required, and economies of scale combined guarantee some considerable degree of consolidation, as with email), but that if it should be capable of it. If it’s not capable of it, it won’t be capable of even limited federation at sufficient scale.