We currently display a virtual ("dummy") MediaInfo entity when trying to access a non-existingMediaInfo page associated with an existing File page (see T137534).
There are several open questions about how far this "virtual" entities should go. Should we consider such entities to exist (so it's just the wiki page that doesn't exist)? In particular:
- should we send status 404 when displaying a virtual entity?
- should EntityStore resolve valid IDs to virtual entities, even if there is no corresponding wiki page to load data from?
- should virtual entities be supported by Special:EntityData?
- should virtual entities be included in dumps?
Note that "virtual" MediaInfo entities are not necessarily empty. At least their RFC mapping (and probably also their JSON representation) would at least contain the URI of the corresponding media file (and perhaps URLs of the file page, the file itself, a thumbnail, etc). Additional information could be optionally included: the media file's mime type, size, resolution, duration, and other meta-data.
Also keep in mind that in the final product, the MediaInfo content would not live on a separate page, but in a "slot" of the file page itself, see T107595.