This is interesting, but seems pretty irrelevant for the real world (kinda like "i = ++i + ++i;" C puzzle). The answer to those dangers is "don't do it then". Use your stdlib to emit json, don't use string functions to modify json, assume any number is no better tha float64, and base64 your binary data - and you will never have to worry about this "minefield"

(the only possible problem is if you are designing a security system, but even then, since all the ambiguity is whether to reject the string, it will cause DOS at worst)