ECH (Encrypted Client Hello) encrypts SNI, which is the only field in cleartext in a HTTPS connection. It requires use of an encrypted DNS server (Edit: no longer mandatory). Enabling this will further protect user privacy by shadowing what WMF sites they are connecting to.
It could also make WMF sites more censorship-resistant. Note that packets with ECH has a distinct signature, so a censor may choose to block it at all.