> Piping JSON through multiple programs creates lots of trivial changes, which makes it hard to do things like take meaningful diffs.

That's the virtue of having a format which offers a canonical representation for data.

> No insignificant whitespace.

I.e., it's not human-readable. It also has no decent way to exchange binary data (there is no byte-sequence type: one must either use Base64 or an array of integers, neither of which is space-efficient).

It'd be nice to have a format which is both human-readable and has a canonical representation. Fortunately, such a thing already exists (and I've even linked to it once already today), and has since 1997: http://people.csail.mit.edu/rivest/Sexp.txt

Here's a JSON example (from http://json.org/example.html):

    {
        "glossary": {
            "title": "example glossary",
        "GlossDiv": {
                "title": "S",
          "GlossList": {
                    "GlossEntry": {
                        "ID": "SGML",
              "SortAs": "SGML",
              "GlossTerm": "Standard Generalized Markup Language",
              "Acronym": "SGML",
              "Abbrev": "ISO 8879:1986",
              "GlossDef": {
                            "para": "A meta-markup language, used to create markup languages such as DocBook.",
                "GlossSeeAlso": ["GML", "XML"]
                        },
              "GlossSee": "markup"
                    }
                }
            }
        }
    }

Here it is in SON:

    {"glossary":{"GlossDiv":{"GlossList":{"GlossEntry":{"Abbrev":"ISO 8879:1986","Acronym":"SGML","ID":"SGML","GlossDef":{"GlossSeeAlso":["GML","XML"],"para":"A meta-markup language, used to create markup languages such as DocBook."},"GlossSee":"markup","GlossTerm":"Standard Generalized Markup Language","SortAs":"SGML"}},"title":"S"},"title":"example glossary"}}

Here it is in an advanced S-expression representation:

    (glossary "example glossary"
              (div S
                   (entry SGML
                          (sort SGML)
                          (term "Standard Generalized Markup Language")
                          (acronym SGML)
                          (abbrev "ISO 8879:1986")
                          (def "A meta-markup language, used to create markup languages such as DocBook."
                               (see-also GML XML))
                          (see markup))))

And here it is in its canonical representation:

    (8:glossary16:example glossary(3:div1:S(5:entry4:SGML(4:sort4:SGML)(4:term36:Standard Generalized Markup Language)(7:acronym4:SGML)(6:abbrev13:ISO 8879:1986)(3:def72:A meta-markup language, used to create markup languages such as DocBook.(8:see-also3:GML3:XML))(3:see6:markup))))

What, you'd like something which is immune to 7-bit/8-bit or email mangling? Here's the same data in transport format:

    {KDg6Z2xvc3NhcnkxNjpleGFtcGxlIGdsb3NzYXJ5KDM6ZGl2MTpTKDU6ZW50cnk0OlNHTUwoNDpz
    b3J0NDpTR01MKSg0OnRlcm0zNjpTdGFuZGFyZCBHZW5lcmFsaXplZCBNYXJrdXAgTGFuZ3VhZ2Up
    KDc6YWNyb255bTQ6U0dNTCkoNjphYmJyZXYxMzpJU08gODg3OToxOTg2KSgzOmRlZjcyOkEgbWV0
    YS1tYXJrdXAgbGFuZ3VhZ2UsIHVzZWQgdG8gY3JlYXRlIG1hcmt1cCBsYW5ndWFnZXMgc3VjaCBh
    cyBEb2NCb29rLig4OnNlZS1hbHNvMzpHTUwzOlhNTCkpKDM6c2VlNjptYXJrdXApKSkp}

All three of those S-expression formats can be losslessly converted to one another. Ordering is exactly as specified (they are lists, not unordered or ordered dicts — although one can understand them as dicts, if desired).