I saw that NTPv5 is now supported on ntpd-rs so I enabled it on our test server ntpd-rs.sidnlabs.nl.
It’s still pretty fresh - I haven’t even double-checked if it’s working properly myself. But feel free to play around with it!
Support is for the draft-ietf-ntpv5-04 I-D, currently.
See draft-ietf-ntp-ntpv5 section 7.1.
For the record; there is also this: https://github.com/mlichvar/chrony-ntp5.