I think its too early to tell if it will be sustainable economically.
I believe it will be sustainable, due to cloud hosting costs going down every year. If the trend continues federation/self-hosting might become the default way to operate software services (even non-social stuff). However, another trend that needs to continue is automation of monitoring and security updates.
In the meantime, if you want to take the fediverse for a spin. I am working on a few aggregator projects to help you explore the fediverse with minimal friction.