Inspired by the similar feature in recording/streaming software OBS (as well as standard video editing software), something that would make widgets easily look slick is by adding a selectable transition that would occur when the widget becomes visible or disappears. We already have a fade, but OBS also has slide in and out of a direction on the screen, wipe, etc. Even just adding a smooth glide in/out of a selected direction on the screen would make widgets look much cooler. The same effect could be reused to apply a transition in/out of loading screens or cutscenes.
Here's an example using OBS