Why not JSON5?

JSON5 is also a proposed extension to JSON to make it more readable.

Its main criticism of YAML is::

There are other formats that are human-friendlier, like YAML, but changing from JSON to a completely different format is undesirable in many cases.

This is, I believe, mistaken. It is better if a language is not subtly different if you are going to use it as such. Subtle differences invite mistakes brought on by confusion.

JSON5 looks like a hybrid of YAML and JSON::

{
    foo: 'bar',
    while: true,
}

It has weaknesses similar to TOML:

• The noisiness of the delimiters that supplant significant whitespace make it less readable and editable.
• The use of syntax typing is neither necessary, nor an aid to stricter typing if you have a schema.