Include journal metadata in JSON/EDN Export

I’m working on a blog/digital garden static site generator that consumes the JSON export format. One thing that would make this much easier would be to include metadata about journals in the properties field in the export such as:

    "journal?": true,
    "journal-date": "2007-03-01"

I’m willing and able to implement this myself, but need some pointers on where to best put the db/page? query and what to pass in.