The point of a deep fake is usually for the fake to say something new and outrageous.
Unless I misunderstood the goals of the study of course.
None of these techniques are out of the budget of a college film or dedicated hobbyist.
And I disagree with you about the lipreading. There's a reason ADR in films is always done with a shot of the back of the actors head.
Even when it's done with literally the same original speaker it's pretty obvious. Or have you never fooled a stranger in the alps?