Individual historical revisions often have significance: as the outcome of a compromise, the version of an article that became a Featured Article, one of two options in a significant format switch.
It is often useful to link back to those historical revisions. It would be even more useful to have a short description of what the revision is. When you aren't looking at a diff, the edit summary isn't evident. And often the edit summary isn't directly about that revision but part of a running commentary throughout the history flow.
An additional field in the revisions table for a subtitle(?), that would show up under the title - perhaps in a different color - would address this. But any way to make a title or brief description visible at the top of the screen would be excellent, and would make the strengths of permanent revisions even more useful.