Thanks so much for sharing! I really appreciate the comment from you and @sheila.rabun about the associated metadata schema being sensitive in the definition. It would be great to hear more about use cases where an associated metadata schema isn’t needed - e.g. using Handles or ARKs vs. another PID.
For our use cases, the associated metadata is key for creating connections between PIDs. For example, we assign DOIs to datasets. In the dataset DOI metadata we want to include the ORCID iDs for the data creator, the ROR ID for the data creator’s affiliation, the ROR ID for the funding organization, an Award DOI for the funding, associated journal article DOIs in related identifiers, etc. Without the associated metadata schema, we wouldn’t be able to create those connections.