> It's both hard for human to format correctly, and for library creator to make a compliant parser.

It is actually very easy to format correctly, unless you don't understand the format. While it may challenging to make a compliant parser, many exists for multiple languages.

JSON isn't a viable replacement.. TOML doesn't support root level lists and has its own set of challenges and is a lot more ugly and difficult to understand for complex nested structures.

If you want to kill YAML then replace it with HCL.