The world desperately needs a replacement for YAML. TOML is fine for configuration, but not an adequate solution for representing arbitrary data. JSON is a fine data exchange format, but is not particularly human-friendly, and is especially poor for editable content: Lacks comments, multi-line strings, is far too strict about unimportant syntax, etc. Jsonnet (a derivative of Google's internal configuration language)…
It's far more productive to push for incremental changes to the YAML spec (or even a fork of it) to make it more sane and better defined. Things like a StrictYAML subset mode for parsers in other popular languages.