ClippedCub
I'm sorry, I wasn't very clear. The idea of banking into the wind was merely to illustrate the presence of the lateral force that needs to be opposed when the aircraft has a slip angle. I wasn't suggesting that it's a good operational procedure. That said, in an aircraft that develops significant lift before rotation speed, banking into wind by lifting the downwind wheel may be the only way of staying on the runway, when the weight on the wheels is insufficient to oppose the slip force. It's just the reverse of a wing-down crosswind landing. There are (at least, light) aircraft that have sufficient rudder authority to remain straight, but are limited by their ability to avoid drifting off the runway before rotation.
Flaperon
I'm afraid I still don't follow your logic. Once in the air, the constraint to align heading with track is removed. The aircraft can simply yaw into wind, and there is no longer an "upwind" or "downwind" engine.