Aspects of this already exist to varying degrees of polish. Conduct a search for pleroma, mastodon, gnu social, hubzilla, friendica, diaspora, etc. and you'll see a diverse ecosystem of platforms. By the way, this ecosystem is referred to as the fediverse (federated universe). Sure, the thousands (yes thousands!) of mastodon servers/instances receive most of the limelight, but mastodon is not the only platform. The old challenge used to be the network effect ("oh, but none of my friends are on network X...")...but with recent stats citing over 2.5 million users active on the above networks...it is just a matter of time when one of your friends will make their way onto the fediverse, pulling you and your other friends into it. So - perhaps a little prematurely - I welcome you to the Fediverse! :-)