With the recent release of the File data type in D365, it would make sense to be able to include fields of that type in the collection returned with RetrieveAllEntitiesResponse. Currently this response returns metadata for all field types except for the new File type, so based on the response object, it's as though no fields of that type exist in D365.

The missing class is documented here: https://docs.microsoft.com/en-us/dotnet/api/microsoft.xrm.sdk.metadata.fileattributemetadata?view=dynamics-general-ce-9

The documentation states that this metadata class is already a part of the SDK, but support for returning FileAttributeMetadata in the RetrieveAllEntitiesResponse does not exist.