Federated media multipart/mixed JSON object shouldn't be required to be empty

[f0x52]

Link to problem area:

matrix-spec/data/api/server-server/content_repository.yaml

Lines 44 to 45 in 2cbf606

	and describes the media's metadata, if any. Currently, this will
	always be an empty object.

https://spec.matrix.org/v1.11/server-server-api/#get_matrixfederationv1mediadownloadmediaid

Issue
MSC3916 point 4 describes the federated multipart/mixed media metadata JSON object as

No properties are yet specified for the JSON object to be returned. One possible use is described by matrix-org/matrix-spec-proposals#3911.

However the spec entry just says 'Currently, this always be an empty object.'

Expected behaviour
Either mention that there are currently no standard fields for the object in spec, or have an explanation similar to other areas in the spec where objects are allowed extending with keys that follow Java package naming convention.
afaik current server implementations already just parse the JSON object but don't enforce it to be empty.

[turt2live]

does "Currently" not imply it could become non-empty?