The simplest solution here would be to use JSON5 (https://json5.org/) if you're after comments.
It still doesn't support / standardize dates, though.
But realistically, it's also all about the ecosystem. VSCode for example doesn't come with JSON5 support out of the box. GitHub and many other tools / renderers and supports it at least in syntax highlighting.
Maybe they should try to file an RFC update/new spec? I would be all for it, since it is backwards compatible and covers some essential new needs of a modern configuration syntax. It seems they already have some notable people included in the project, making it more plausible to succeed as a succession to RFC8259.
It still doesn't support / standardize dates, though.
But realistically, it's also all about the ecosystem. VSCode for example doesn't come with JSON5 support out of the box. GitHub and many other tools / renderers and supports it at least in syntax highlighting.