This post by Terence Eden seems to me to be a very good prediction of where the Fediverse is headed, should it actually take off:

→ How much decentralisation is too much?

There might be a dozen different phone networks in your country. Yes, they Federate with each other, but they all happen to be running close-to-identical networking gear made by Nokia or Huawei. Yes, you can put your SIM in any device, but chances are it is either Android or iOS.

We’ll be stuck with the illusion of Federation.

Thanks to Евгений Кузнецов for the link!