As of now you get parse errors for common modern/human-readable JSON config usage - trailing commas, comments, etc. Changing extension of some of these files is impossible because they belong to external tools that expect .json, yet are able to parse/interpret it correctly as either JSON5 or JSONC. Examples: bunch of configs related to VSCode and its plugins.

Overall JSON standards are a mess because the initial standard sucks and it's hard to have consensus now, but would be nice for tools like this to support as many valuable options as possible.