Is this thing bound to fail? https://aralbalkan.com/notes/ello-goodbye/ and http://meta.ath0.com/2014/09/25/interested-joining-proprietary-social-network/ strongly suggest that, but is that a problem? I don't think so.
The main problem in today's social network landscape is not that things are proprietory or that network owners are less than 100% honest - the main problem is monoculture. To break the monoculture of Facebook, we need to see new takes on how to do it, and some of these may very well have ambitions about being "the next Facebook". And perhaps they will prevail. And after that we will flock to yet another platform. And we may even at some time in the future see a world where Diaspora is more than a pipe dream.