I'm an app developer. This change will absolutely break some of my stuff, and it's going to suck. Even with that, I do feel OP is taking an overtly political stance (even using the word "banned".) This change is perfectly reasonable within the already-strict mindset of Swift. Having a less-strict language just to work around potentially buggy Apple frameworks would be setting a bad precedent.
Using "final" also has some performance wins by reducing dynamic dispatch. [1]