Implicit conversions should be, in my opinion, used very sparingly - generally they should only be used for DSLs, and DSLs should only be used to reduce boiler plate in very common situations.  I don't think converting JSON to ascii is a very common requirement, so I'd rather keep it simple and not have the magic.  If for a particular user, it's very common, then there's nothing stopping them from adding a simple implicit conversion to their own code.