Keyframe Slice editor
Would it be possible to keyframe the slice editor to track a moving shape on a video?
No, it's not possible.
But what is the purpose ? Tell the story, there may be a solution other than the one you think about.
You can do a lot with a solid layer (color card) with an alpha matte (blend mode). You can animate this layer with mapping keyframes.
Suddenly, the layer (with your content) below can also be animated with keyframes.
(Sorry for my english)