I want a version control/edit history browsing interface that lets you view your file as a 2D image extruded out into 3D space into the time dimension. Instead of seeing spans of text crossed out and added, you just see them appear lower down the "time stack" and disappear higher up. And then I can imagine scrubbing through slices of this time stack with a dial or a scroll wheel like scrubbing through slices of a CT scan.

I like this because it gives physical materiality to answers to abstract questions like "how often does this file change"? or "Which of these changes were more persistent"? or "Are there more additive or subtractive edits to this project in the last month?"