It would be useful to store the Phabricator username in LDAP. This would allow to validate the NDA status as stored in Phabricator.
This isn't needed anymore. NDA management has changed towards a new workflow which doesn't rely on Phabricator any longer.
One remaining use case if for the offboarding script (which currently passes the Phabricator name as an argument). But since a Phab account can either be linked to a wikitech name and/or a SUL account and we have T148048 to store the SUL account in LDAP in the future, we can simply rely on that.