Is decentralised federated social media over engineered?

Can’t get this brain fart out of my head.

What would the simplest, FOSS, alternative look like and would it be worth it?

Quick thoughts:

* FOSS platforms intended to be big single servers, but dedicated to …
* Shared/Single Sign On
* Easy cross posting
* Enabling and building universal Multi-platform clients.
* Unlike email, supporting small servers

No duplication/federation/protocol required, just software.