The new feature shows a line where a drag started and where it will end. I don't understand what you mean, as it doesn't make sense to show this for the last frame of the animation.

In Spine, the size of your selection box is important. When scaling keys like in your videos, you should make your selection box the size of the keys you want to scale.

Say you are scaling keys on frames 0-30 and you want to make it 0-60. If your selection box is 0-30 then you drag +30 frames to 60. However, if your selection box is 0-40 you will have trouble scaling the keys to 0-60. Moving +30 frames is not enough! You will need to move +41 (due to rounding). This is because when you are scaling the box selection, it is scaling the size of the selection, not moving the keys a certain number of frames.

The orange numbers show where you started dragging and where you are dragging to. I believe I understand your suggestion to instead show where the last frame of the animation was and where it has moved to, however this would be different from what the orange numbers mean in other situations. I think it's better to make your selection small, matching the size of the keys you are scaling. That gives you what you want and allows the orange numbers to always show the same thing: where you started and where you ended the drag.