I would say JSON + schema, rather than just JSON. Like S-expressions, JSON saves you from having to implement a tokenizer, and a tokenizer is one of the easier parts of a DSL. You still need to implement something like a syntax, because things that are handled by the syntax now get pushed into later stages of the DSL. However, if you can provide a JSON schema for your language, then the problem is mostly solved !

On the other hand, it's not enough to read JSON, you need a JSON parser library that provides you with the position (line:column) of every JSON value, so that you can emit user-friendly errors.