Related to Text changes in Fields are not included in Undo (and should be), I think another feature needed for the Undo system is “Redo”, i.e. a full ability to move forward/backward in change history. This is common in many other apps and very helpful, especially for reversing accidental Undo. It is generally an expected feature in my experience.
So Ctrl/Command-Y should “redo” (revert the last undo action).