This is great feedback.
I'm coming away with 3 things:
(1) DIT Structure Rules are the standard way to enforce DIT organization.
(2) DIT Structure Rules are supported by few LDAP implementations today, but OpenLDAP and other implementations plan to add support for DIT Structure Rules in the future.
(3) For the FedFS standard, it would be useful to describe optional (but not required) DIT Structure Rules.
-james