I could easily imagine a functional-programming JSON transformation language, or perhaps even a JSLT based on latest XSLT spec. The key in these things is to constraing what is can do.

We wouldn't even need anything as complex as XSLT, or a functional language for transforming JSON. Other markup-based template processing systems exist for higher-level languages like Pug, Mustache, etc. for Node.js. You could achieve a lot with a template engine in the browser!