Better than nothing, but the problem with that is that you can't construct a deep, lazily evaluated pipeline. JSON can't be outputted until all the data is collected.
That still limits us too much due to the rather severely limited available data types (although arbitrary types could be serialized into binary/string data, I guess...)
Funny that you should mention this. I just hit that problem yesterday. The lack of a binary type is a problem. This is the same thing that hit XML. Unfortunately (or fortunately), the best solution is still the MIME stuff.