One other aspect of Rust that makes it suited to GUI work is the fact that the management of mutable state is one of the core problems of writing a GUI app, and that Rust allows you to talk about mutation in a way that no other language (that I know of) does. You can a) have mutable structures, and b) declare that a function will treat one of those - passed as an argument - as deeply immutable, both within the same language. You can have exactly the amount of mutation that you want, which should be extremely enticing to any GUI developer.
Not really true, because the "interior mutability" pattern allows for mutating structures that are passed via a shared reference. Truly "immutable" data is in fact quite hard to characterize in a language that's as 'low-level' as Rust.
Technically yes, there are trapdoors like RefCell. But these are intended to be used sparingly because they move all relevant borrow-checks to runtime. Under normal circumstances immutability is statically guaranteed by the ownership system, which is much more than can be said for other languages where mutability is an option at all.
I suspect lifetimes get you the vast majority of the benefit of immutable data for UI purposes, tbh. It lets you ensure that references aren't retained or accessed at the wrong time, unless they provide an explicit way to bypass that (i.e. the defaults for data types is safe).
