The browser only reluctantly accepts its role is an application UI platform. Every problem, including the ones you describe, come from the disconnect between what a browser is and what it is used for. The browser is always going to lag behind user expectations so that's why I think it's the last place we should put that functionality.

Adding more high-level UI functionality is really in conflict with the idea of browser as platform. Other features, like WASM, are pushing the browser the other way.