A Modest Proposal that will never be implemented: add an interface to String, Boolean, Integer, Long, Float and Double. Because all these types already implement "toString" (and I believe their toString representations are compatible with JSON), it can be a pure marker interface.
> I believe their toString representations are compatible with JSON
Not quite. String is the big problem, since it needs to be wrapped in quotes, and special characters need to be escaped. But Float and Double are also problematic because Infinity and NaN aren't representable in json.
However, the new interface could have a "toJsonString" or maybe even a toJson method that returns a JsonValue
