Not that. More like, UX paradigm more fixed and forced on applications, but also being customizable and user-programmable externally to any given application. So that e.g. you could have a system-wide autocomplete/code completion, whether you're in a code editor or text editor or in a dialog box of some other program somewhere; that system-wide autocomplete would be configurable and trivial to extend or replace wholesale with another widget.

This is a reality within Emacs (which really is a 2D text OS running lots of applications inside, including a text editor), and being text-based does play a role. When it's very hard to draw arbitrary pixels on screen and most of all apps deal with text, it's easy to make a large set of very powerful interface tools, and it's easy to pull data out of an app and put data into it, whether the app intended it to happen or not.

In the back of my mind, I sometimes wonder how something like Emacs could be made with modern browser canvas, to enable cheap rich multimedia, while retaining the ability for inspection and user-programmability. Introducing arbitrary GUIs is hard, because next thing you know, half of the stuff is drawing to canvas directly and it's all sandboxed away from you.