I got the impression from what I saw (coming into the scene a little too late to say from direct experience) that languages like C++ and Java, intentionally or not, did a great job of capturing how procedural programmers implemented the thick, rich, stateful GUIs that were common at the time. GUI widgets were literally the textbook example that many books used to explain classes and inheritance in a way that procedural programmers could relate to. So, I would say that the OOP style of GUI programming was a continuation of the procedural style that brought the old way of thinking to new "heights" through the new OOP language constructs.
Yes, GUIs have both been greatly benefited by the availability of OOP and a great force on the popularization of that paradigm. I think nobody will disagree that GUIs are kinda hard to create in purely structured code, and OOP makes compares much better.
But we are not at the 80's anymore, and have more options now. There is very little you can do with OOP that you can't in Rust, and a whole lot of things Rust adds to it. Just because things evolved this way it does not mean they are optimal.
Rust is great, but it can't do very basic things that OOP offer. You can't make a simple observer in Rust without RC<RefCell<T>>, unsafe, global-ish mutable state, or being forced into some framework.
You can always copy the observer into the observed structure (and avoid a lot of complications - observers are best created with FP, not OOP). You can also carry the GUI and whatever else you want as a parameter when executing the observer.
But, of course you won't be able to mutate arbitrary global state.
