We want to have Wikidata as a central part of the linked data web. This means we need to not just provide the bare identifier (m1234) but also the complete concept URI (imdb.com/m1234).
These properties would be covered: https://www.wikidata.org/wiki/Special:ListProperties/external-id
External identifiers should be treated as resource references in RDF, if we know how to construct a URI from the id in the DataValue.
Such URIs con be constructed based on a URI pattern stored in the property_info table, extracted from a Statement on the property page, just like the formatter URL.
See also the relevant design document.