Analogous to /isbn, there is a widely used identifier called EIDR ( wikipedia, wikidata ) which we don't have a property for in schema.org.
I propose fixing this, using the same definition as Wikidata: "Identifier for a film or television work, edit or manifestation, in the Entertainment Identifier Registry".
According to Wikipedia, it is applicable to a wide range of entity types, so I suggest associating the property simply with CreativeWork.
"The identification system resolves an identifier to a metadata record that is associated with top-level titles, edits, DVDs, encodings, clips, and mash-ups. EIDR also provides identifiers for Video Service providers, such as broadcast and cable networks.
In terms of expected adoption, we would expect to make some use of this at Google.