And assuming people want deeper integration is the browser even the right level of abstraction? Arguably it would be better to have something that was operating at the OS level, like siri/gemini assistant style.
If a global LLM becomes standard, I'd want to plug in my own local model or disable it entirely, but I don't think Microsoft nor Apple are going to open up their operating systems and make it easy to do that any time soon. The option to granularly use your own models is a plus to me in that situation.