Sure, I can see how it would be useful, but wouldn't you prefer to have the choice of which AI to use? What if Brave's AI is worse than Chrome's, which is worse than ChatGPT? Or what if it's better, and you're now tied to that browser, even though you'd otherwise use something else?
Even if I had this functionality built-in, I would still prefer to use something else. Even if that's slightly more cumbersome, though there will probably be extensions for this sort of thing, if they don't exist already.
But, to each their own. :)