IMHO a modern terminal should render things on OpenGL surface. If done well this should be quite lightweight but at the same time could allow some amazing rich terminal apps. Something like "give me this 30x10 region and I'm going to render whatever I want in it"
I could type "df --HISTORY 7 /filesystem" and it renders a graph showing the last 7 days utilization. Yeah, df would need to change.
Or we could write "thumbnail babes.jpg" and it renders it directly in the terminal instead of popping up another window.
Or if I'm wanting to do some scripted image editing it'd be pleasant to be able to render images directly into my terminal as I work out the specifics of my task. As opposed to writing to temp files and then viewing them with a separate viewer.
Personally though what I want from a terminal emulator is something integrating into SSH which creates an out of band channel from the remote end of my ssh session to the terminal emulator. This way I don't have to play stupid games with shell prompts and the like, programs could literally know that a data path to my screen is available and do things like change background colors if I've changed users. Messing around with prompts and shoehorning too much stuff into escape sequences is awkward.
The command line interface is nice for advanced users as it's like programming. But for normal computer users that just want to get shit done, a GUI is much better. For GUI I recommend using a window manager and a large dedicated desktop monitor. You can have your image in one GUI window app, that auto reload the image when the file is updated. And have the code editor in another window app.
