[Standards] Re: Proposed XMPP Extension: End-to-End Encrypted Contacts Metadata

To be honest, I don't understand the "encrypted roster" discussion. Even if the server does not see the roster at all, it is able to fully infer which jids are part of a user's "roster"

Absolutely. For most clients/apps developed as they are today this is not useful and would not be used. But if you were making a specially handled client that eg did not send or request presence from anyone, did sealed sender / sealed recipient with a TBD onion routing XEP, and other things then this could be a useful building block to still allow syncing contacts between multiple such apps instead of having them just local. We may be going cart-before-the-horse here but OTOH having a building block isn't bad.