> The only thing that JSON is really missing are comments and trailing commas. I use JSONC for that.

YAML[0] supports JSON formatted resources and octothorpe ('#') comments as well. I didn't see anything in the spec specifically allowing for trailing commas however.

Here is an exemplar using the Ruby YAML module:

  #!/usr/bin/ruby
  
  require 'yaml'
  
  
  puts YAML.load(
    %/
      # YAML is a strict superset of JSON, which
      # means supporting octothorpe end-of-line
      # comments is supported in JSON formatted
      # YAML if and only if the content is multi-line
      # formatted as well (like this example).
      {
        # This is valid YAML!
        "foo" : "bar"
      }
    /
    )
  

0 - https://yaml.org/spec/1.2.2/