Could be that I don't understand the story correctly, but isn't this exactly what we've decided in T141254 that we don't want?

I think T141254 was fixing something that was not logical for some people (compare revision to itself). It must not be illogical to show a single text.
However, not running in T14154 should be considered; it also should be discussed if this would be in the features scope anyway. As for now, I do not know an actually existing workflow (in contrast to a made up "maybe they want to…" one) that demands this function.

Ok, then I do not fully understand the story. RevisionSlider is shown on Diff-Pages, so showing "no diff" would be kind of illogical after all. Also, there's always a single revision shown on the page below the diff. The story does not explain which version should be shown. The one selected with the right pointer or the one selected with the left pointer? The software glitch from T14154 unintentionally allowed showing just one revision without a diff (or better: with a null-diff), which, IIUC, is what the story requests.

As I see it the use case is not about comparing the same revision. It's about jumping to a revision and looking at it. The RevisionSlider helps to avoid going forth and back on the history page but in some cases its not able to replace it completely. ( I know that was not the original task, but I have the feeling people now see the tool like that or want to use it like that )

We allow the selection of revisions and to compare them. We do not allow comparing the same revision, since it makes no sense. But we do not offer the possibility to just see a specific revision like you could on the history page.

A simple solution to solve this would be re-allowing the comparison of two revisions.

Another one could be adding a new option to jump to a specific revision of a page ( and leaving the diff page and the slider ).
e.g. https://en.wikipedia.org/w/index.php?title=Bread&oldid=752025506

Since a single revision is always shown below the diff, another possibility would be to provide a way to jump there or make it possible to e.g. collapse the section with the diff.
Leaving the diff page and the slider would probably not enhance the situation that a user would have to go back-and-forth between two pages.