I hope I'm wrong, but... I think network effects could lead to a single instance becoming dominant and therefore vulnerable to such a takeover/sellout. I'm less sure about this, but perhaps non-technical users don't understand the concept of federated instances and flock to a single one. Perhaps there are other tangible benefits of everyone being on a single instance. Just because the protocol allows for decentralization, doesn't mean it will naturally happen. E.g. How many email users are on Microsoft exchange/outlook, Gmail, and Yahoo?
I love the concept of your own data being portable, but am afraid there might be other factors that somehow naturally lead to centralization. Please change my mind!