It would be very useful if AI could do it (though I kind of doubt something high-performance can be created this way). It's economically unfeasible for humans to develop a browser engine from scratch anymore. Microsoft and Opera gave up. Apple probably will too someday.

It's the most complex piece of software on your computer (it's basically an entire sandboxed operating system, at this point), the standards it has to adhere to are expanding every day, its performance optimization is critical yet adversarial (i.e. website owners have no incentive to make their sites efficient - the browser will be blamed for slowness, not them), and it costs the user nothing. No company can afford to maintain that, unless it's serving some broader strategy that's earning billions.