The most important part of a social network is the people on it. A decentralized social network will never be able to compete with the marketing of for-profit social networks like Twitter and Facebook. Without marketing, you will never get a critical mass of people on it, which means your social network would be missing the most important part of a social network.

At best you end up with a little hangout for you and a handful of people you already know, possibly people who were already on the mainstream for-profit social networks with you but you insisted they use this other one to contact you. At that point you have an overengineered group chat application.