I can tell you what happens: the car slows down.
You can mash your foot to the floor, be doing 80mph, and put the car in neutral--and nothing happens other than the drive system disengages and the gas engine stops running.
In the meantime, your foot is still mashed onto the floor, imitating an errant floor mat.
I know this because I did it last week.
Why would you think that "it might not be pretty"? What did you expect would happen?
Do this in a BMW, and the car similarly starts slowing down because, just like in the Prius, the drive system is disengaged.
Sure, the BMW engine will start screaming and bouncing off the rev limiter, but it won't be damaged. All you'll experience is a lot of noise--but you'll be in control of the car.
What did you think would happen?