It will be open source, end to end encrypted using Signal’s double ratchet encryption protocol, and he plans to make it easy for fediverse platforms to integrate it. The beta will release later this month.
He’s also the creator of https://fedidb.org btw
In the end any successful chat service is going to be used by horny teenagers sharing nudes with each other, which is honestly for me better reason than any state secret why all communications should be end to end encrypted at all times. I don’t trust Zuckerberg or Musk with that, or any other third party for that matter.