Instant visual stepping through undo history

Problem

When I tweak materials or lighting, I often want to compare the appearance before and after the change. But each change triggers a refresh in the viewport, which takes a while, so I can't always see whether the change has made the scene better or worse. To compare before-and-after, it's best to be able to toggle back and forth instantly.

Idea

Each time I make a change, store the viewport display in a cache, and provide a UI to step through these visual records of what the scene looked like with each edit. For instance, I could hold a modifier key and use the mouse wheel to step through the undo history, then release the modifier key to revert to the version I'm looking at, or right-click to cancel.