Do you mean passing around binary between backend services and then having a binary->JSON "proxy" behind whatever is receiving AJAX requests from the client?
My idea was that the client (HTML+JS) will transform the binary data into JSON or skip the conversion and process it directly. Seeing how fast JS engines have become and the amount of typed binary arrays processed in JavaScript, I believe it's a viable approach. But I'm not a frontend dev, so I can't be certain.