> a full monospaced information-dense UI framework, a terminal designed for user interfaces, rather than one designed to replicate the limitations of dumb terminals?

I can only speak for myself but I use the CLI and TUIs specifically because of the limitations those modalities impose on software that uses them as the primary method for interfacing with the end user. If you want a full featured UI and all that comes with it why not just use QT or GTK or modern HTML or etc?

I think the only "improvements" I'd like to see are thing such as metadata regarding what the different streams are for, an official way to communicate using structured data as opposed to raw bytes, that sort of thing. Spiritually in the same ballpark as the difference between HTML before and after CSS.