That's effectively what hybrid cars do.

Essentially regenerative braking. Should work, though the question is how coat effective.

F1 has been using this principle for years

That's just regenerative braking on a bike. Without batteries.

In theory that idea isn't actually bad although I suspect in practise the mechanism would be extremely complicated and would be liable to jamming it in opportune moments. That said doing this electronically is already a thing, although not really in e-bikes.

Dynamo lights work off a similar principle. It extracts energy from pedaling or the wheels spinning to power lights on the bike. You can feel the drag and it's probably about 5w of power. Really not a whole lot. About the same energy you'd save from wearing smooth socks or cleaning the chain for some perspective.

The extra weight required to implement a solution like yours would probably rob the rider of any gains. But in a very theoretical sense it could work if the material weighed an insignificant amount.

Why flip a switch when you can just let the bike sense if it is going up or down hill?

Would make hilly terrain a much smoother ride.

Then again, if you do all that electrical, you already just have an electric bike. Which is even more versatile on flat ground.