RDF 1.1 JSON Alternate Serialization -- Note

Looks like .rj rdf/json files are now a standard.

If I'm correct data.fm and rww.io (among others) use this?

Suggested mime type: application/rdf+json

Wondering if it's an idea to add that mime type

Note: unless you have a specific reason to use the syntax defined in this
document instead of JSON-LD, you are encouraged to use JSON-LD.

http://www.w3.org/TR/2013/NOTE-rdf-json-20131107/