The lightening rear is an interesting thought. It would take some pressure off the rear tires, shrinking their contact patch a bit and reducing rolling resistance down a straight (I think). It could have potential tire wear benefits (in the rear). It may even effectively increase the diameter of the rear wheels a small amount (at peak speed since they wouldn’t have so large of a flat contact patch), effectively being a nano-CVT adding a little top speed. The effect would likely be very small, but measurable.