The problem succinctly is when the terminal emulator only sees cell values and instructions it can't do anything more with things. Two really good examples are implementing accessibility well, and scrolling / changing things above the terminal pane without rewriting the whole history.
What you describe sounds a lot like the HTML/CSS split, with having a separate semantic/display data. I think that's a rather large jump from the 80x25 model, retrofitting that much data sounds like quite the challange.
Not sure how you're planning on doing that, can you incrementally extend the current model, or will it require a completely new protocol?
New protocol entirely. The existing stuff is too baked as having positioning, movement, cells as the unit of abstraction. You need to have that available, but not as the core abstraction level. The core has to be areas, words, layout, etc. Not: "move to 20, 35, start red, bold, print border characters"
It's mostly something I'm thinking a bunch about recently. Nothing written up yet aside from the above. I'd go read Mitchell Hashimoto's Lobsters interview fora different take and see how that resonates with you as well as the recent blog posts about TUIs and accessibility.
