S-expressions are super easy to parse and are fairly easy for humans to read. See e.g. using s-expressions in OCaml: https://dev.realworldocaml.org/data-serialization.html
My feeling is that :keywords reduce the need and temptation to conflate strings and boolean/enumerations that occurs when there's no clear way to convey or distinguish between a string of data and a unique named 'symbol'. I miss them when I'm in Pythonland.
[1] https: https://www.compoundtheory.com/clojure-edn-walkthrough/
You get neat ways of nesting data, but that is not enough for a robust and mistake-resilient configuration language.
The problem isn't parsing in itself. The problem is having clear sematics, without devolving into full SGML DTDs (or worse still, XML schemas).
Hm, not sure that's true, S-expressions would only define the "shape" of how you're defining something, not the semantics of how you're defining something. EDN https://github.com/edn-format/edn for all purposes is S-expressions and have support for custom literals and more, to avoid "the trouble with data types from JSON"
The tag system is quite brilliant though.