Per the discussions at the 22-Oct-12 working group meeting at Google, this pertains to the different layers of MTI features. For OPs, there will be different sets of MTI features for "open" systems (another possible term suggested is "dynamic") and "closed" systems (other possible terms are "static", "pre-negotiated", and "out-of-band").
This is largely a subset of issue #604 (All - Create a MTI section), but is being left open until this and #604 have been resolved in the specs.
John believes that none of these elements are mandatory. Mike will review while writing the "Implementation Considerations" section. Some do need to be there for common profiles, like the public key.
It seems to me like these elemenets are candidates for being REQUIRED: version, issuer, x509_url, id_token_signing_alg_values_supported, response_types_supported, subject_types_supported. A case could also be made for scopes_supported, claim_types_supported, and claims_supported.
Let's discuss this on the call.
Mike will make the first list REQUIRED and the second list RECOMMENDED