> More people should run their own mail servers so that centralized players cannot control what should be a decentralized communication protocol.

This plan relies on a meaningful number of people voluntarily switching to a setup that requires more expertise and effort for a worse experience in the hopes that eventually large corporations will take notice. That seems like it is unlikely to be successful.

I suspect that if the Europeans or Californians don't force email interop via regulations, it will eventually be an open standard in name only.