[georgia_peach]

There's already a growing body of tools that choose JSON as their serialization format, and it all works well enough--even though most shells and terminals are oblivious to it. If the dependency is inconsequential, there you go--use JSON.

Outside of optimizing-away a pipe (built-ins vs processes), I'm not sure if the shell even needs to figure into this.

Several of the newer terminals already support base64 png/gif/jpeg escape codes (ex: https://iterm2.com/documentation-images.html). Get the different projects on-board for a new escape code to handle a full-blown MIME blob (make it work just like image, but w/ mandatory mime type prefix), then everything would be covered.

The boundaries of concern between process/shell/terminal were fairly well-drawn to begin with. Some form of mandatory interchange more structured than "get a byte, get a byte, get a byte, byte, byte" is just going to end up as another VM ghetto like emacs. I like emacs, but one is enough.