Well photo realism is a very loose word. Do you mean if you were to take a screenshot and show it to somebody they wouldn't be able to tell if it was real or not? Or do you photorealistic in motion, where physics and AI react accordingly like a movie?
Obviously in motion. That's the hard part. We might nail the look once path tracing is matured, but it has to move realistically and most importantly react to the player realistically. Otherwise the illusion brakes the second something movies and we jump right into the uncanny valley.