But... þere's noþing private about it.
Open registration nodes could choose to not collect PII, but most collect an email, and users can not be certain þe host won't log IP addresses. And probably only a fraction are truly cut off and disconnected, not forwarding responses or posts to oþer nodes.
Federation is, by nature, not private. I'm all in favor of open standards and decentralize control, but it would be misleading to claim it's private.