Web folks love JSON and rightly so, it solves many things in JS-land. It is not a useful message format if you are interested in high efficiency or small message sizes. In those cases fully binary messages are the way to go, of course.
If there were two things I would tell the web devs at my employer, they would be these: There is no universal message format that does not already exist, and web tech doesn't solve non-web problems better than non-web tech.
Bonus third thing: JavaScript rots your mind. Avoid it.