It's already in upstream. But the copy on IETF hasn't been updated to reflect the one scheduled for the end of this year. The next step is to update ntp.conf to use that file.
IIRC cy is working on this?
Revision r294773 (updated by r294884, r295495, r300638, and r300638) already did this. I don't understand why the submitter of this PR believes this needs to be done when the code to automatically update the leap-second file is already there. Maybe he can explain why.
r303160 updated /etc/ntp/leap-seconds from ftp://tycho.usno.navy.mil/pub/ntp/leap-seconds.3676752000. No newer version exists.
Most recent copy already in src tree.