Maybe you could even skip the commas entirely (or threat newlines as commas if possible?) That, along with unquoted keys, would make JSON perfect for me.

In such a hypothetical format, eliminating nulls entirely should Also be considered, the difference between a missing key (undefined) and a null value is significant in JS, but other (particularly statically-typed) languages struggle with differentiating those two cases, and this leads to `serialize(deserialize(a))` representing a different document than `a`.