I think animation keyframes should have an "Ease InOut" feature which defines what percent of the time the animation is accelerating and decelerating. For example, if I use the "Position" video effect, add a keyframe at the beginning of the clip with any value, and then I add another keyframe at the end of the clip with a different value, it will cause a jerky motion. So, with this new feature, I set the Ease InOut value to e.g. 20%, and the animation will quickly accelerate for 10% of the time at the start of the clip, move in a constant speed for 80% of the time, and decelerates the remaining 10% of the time at the end of the clip.
If the Ease InOut value is 100%, the animation will always either accelerate or decelerate.
What do you think?
NOTE: I'm not talking about making curves!