The 10-12% thing is a complete myth it's laughable that people believe that. Every part of the brain has centers used for specific tasks be it involuntary like heart rate, breathing, metabolism or voluntary like movement. No part of the brain remains unused.
That may be so but a simple google search explains how that myth came to be.
This was a stupid joke really, Donald Trump may be many bad things but he's not an idiot. He's a self made millionaire last time I checked which is a lot more than anyone else can say.
The point of the bicycle is to go somewhere faster and exercise at the same time so my guess is no unless they make something that does those two things better.
Every technology will eventually be a thing of the past.
I hope not, bicycles are always fun for kids, the way things are going maybe everyone will be on a bike rather than a car due to fuel price and availability.