I don't understand the "Requirements Met" section, that reasoning applies to almost any programming language. You chose Common Lisp because there's a JSON library?
A lot of these intermediary languages are not trivial to parse safely and are a vector for exploits. It's not something you can really do on your own unless you're just supporting a specific subset for your application. Even then, you really need to know what you're doing.
There's a section "hunt for new Lisp". It isn't explicitly stated in the requirements maybe because it can be inferred from there that being a Lisp is also one.