I think it already is kind of like that. The faster you move, the more your enemies will glance on you.
No, the faster any of the parts moves, the higher the speed bonus and more damage, so less glancing. The glancing comes if you use your footwork and place yourself so they hit you very early in the animation, which due to the sweetspot mechanic makes it glance.
So, if you have an enemy moving left to right in your screen, a left swing will have a very low speed bonus (both targets moving in the same direction, so their relative velocity is low), but a right swing, if it hits fine, it will have a very big speed bonus
A clear example is cav, if you hit them at full speed (and your blade is moving in the opposite direction to their movement), or HAs shooting backward at chasing cav, the damage bonus is huge, thats why sometimes cav get 1hit even in heavyish armor when at full speed