I still believe this approach is not optimal in the practical sense. I believe the issue is having a common and standard source of truth for user metadata. So

I still believe this approach is not optimal in the practical sense. I believe the issue is having a common and standard source of truth for user metadata. Social platforms are secondary to this problem. I would suggest we come up with an authentication system that can scale across several small technical groups of people, perhaps something like OpenLDAP. Then lets put a few gateways in front of it like SAML2/OAuth/whatever. Set up replication between a few technical folks in a small circle of trust. If a friend leaves the circle, exclude their node from replication. Now put whatever trendy web app, chat app, misc app in front of that authentication. The apps can come and go, but the authentication data, email contacts, phone numbers, all maintained in one authentication system and highly replicated. Each application should be coded in such a way that users own their data and are prompted to download backups. Data retention policies should be very obvious to the end user and they should know this is not a long term archive for their binary data. Each small group of technical folks share their platform with their circle of technical and non technical friends. Each geek pulls a copy of the backups in the even a friend wants to leave the circle. Different geeks in the circle can manage different pieces of the platform or different applications. At least, that is how I would approach this problem. YMMV.