I generally like the idea of tabular text files where the last column is free form text.
If you need more commenting freedom or flexiblity, why not make another indirection and generate the data from some source which is tailored to your needs? After all, relational data is often not suited for manual input. It's meant for general consumption by computers.
For example, as a sysadmin, passwd / shadow / group is not enough to model my business objects directly. I keep my business data in a custom database, and generate the text files from that.
A very general format could solve more problems but as I said earlier I think the lack of comments in json makes it sub par as a config format for human editing.