Declarations of schema elements should be published as specified in RFCs.

RFC 4512: Servers SHOULD provide definitions of all schema elements they support in subschema (sub)entries.

The definitions themselves, such as for postalAddress, should be generally viewed as immutable. Only certain additions (alternative names and extensions can be added, and DESC values changed. Matching rules should never be changed.

If the equality matching rule is not implemented it should not be

announced in the subschema. Assuming you mean that the "EQUALITY caseIgnoreListMatch" should be removed, no. If caseIgnoreListMatch is not supported, than the MatchingRule definition for caseIgnoreListMatch should not be published.

The server should not simply report what might have been defined in

some RFC. No. See above. I note that the specification does allow publication of unimplemented descriptions. It actually legal to publish caseIgnoreListMatch. But OpenLDAP has traditionally only published supported descriptions.