To be honest, I don't know. All I can say is YAML parsers exist and it works well enough for many applications, although I do understand the issues with it. Sure, it isn't perfect, but no need to re-invent the wheel for marginal improvements.

I roughly agree with the arguments laid out in PEP 518, even though the array of tables thing is not at all "obvious" to me. And I actually do think an "official"/semi-official YAML subset would be great for loads of use-cases - yaml.safe_load already is that in practice.