For raw data type of applications, it's definitely important to be able to preserve pipeline oriented use-cases like `cat img.png | convert-stdin-to-jpg | convert-stdin-back-to-png | imgcat`. But in the hypothetical world where all CLI I/O moves towards JSON, I'd still argue this is not only possible but now strictly easier because you can just explicitly embed mimetype info + b64 instead of assuming/detecting encoding or requiring user to specify it, or working with heuristic file-magic. (Jupyter notebooks work like this to persist images instead of just flat text.) And presumably a smarter suite of JSON oriented tools like jcat/jless would either actually display that data, or notice the type and avoid spamming the screen with raw b64.
That can be helpful, although JSON is still a bad format for this, especially since now it requires base64 encoding. People think JSON is a good format but it isn't. (MIME is also not a very good format for identifying file formats, since you can only specify one format; although there is a "added on" specification like "+zip" and "+der" this isn't very good.)
