For a human-readable, schema-free data representation, I really like Amazon's Ion format (disclosure, I'm an Amazon employee). It is basically JSON + additional types (integers, timestamps, symbols, sexpressions), and support for humane features like trailing commas and comments. It also has a more efficient binary representation. I think it could have been a contender had it been released a decade earlier, but now I think the existing formats are way too entrenched.

https://amazon-ion.github.io/ion-docs/index.html