I wonder if end-user apps will eventually solve this. Conceptually, rather than server admins choosing what's federated, users will have several/many accounts

I wonder if end-user apps will eventually solve this. Conceptually, rather than server admins choosing what's federated, users will have several/many accounts and they will choose what they want, and under the hood that will be enabled VIA whichever server/account they have accesses that community.