New information has come to light: apparently, the March 2020 update will NOT change the default settings for LDAP connections, but another monthly security update will later this year.
ADV190023 | Microsoft Guidance for Enabling LDAP Channel Binding and LDAP Signing: https://portal.msrc.microsoft.com/en-us/security-guidance/advisory/ADV190023
Windows Updates in March 2020 add new audit events, additional logging, and a remapping of Group Policy values that will enable hardening LDAP Channel Binding and LDAP Signing. The March 2020 updates do not make changes to LDAP signing or channel binding policies or their registry equivalent on new or existing domain controllers.
A further future monthly update, anticipated for release the second half of calendar year 2020, will enable LDAP signing and channel binding on domain controllers configured with default values for those settings.
Administrators can prevent the feature update from making those change either by enabling LDAP signing and channel binding NOW or by configuring non-default values prior to installing updates that enable LDAP signing and channel binding by default.