[Animats]

So, in the end, you have a system which allows a JSON data structure to call arbitrary C++ functions. Is that a good thing? That JSON is now highly trusted. And do you really want to program in JSON?

This is essentially a rather complicated way to build an interpreter for another language. To display web pages. Sort of like PHP.

This might be worth the trouble if you were using it to allow programmable shaders in a renderer. Those are usually composed of functional blocks strung together, they have to go very fast, and they're composed by people who are artists, not programmers, often through some GUI. There, it might not be overkill.