The Authors window displays the Author/s, #Objects and % on selecting objects.
It would be useful to also display the date of the last edit of that object for each author instead of opening the history display.
I thought it did display the date a long time ago but unsure.
Can the window display be tweaked to add the date?
You need to create a JOSM ticket for such enhancement suggestions. Here in this wiki it will not be read by developpers. https://josm.openstreetmap.de/newticket
However I think your idea is not really possible to implement as the list lists authors not objects. If it would list objects you could display the last edit date for each object, but which date should be displayed if one author edited 50 objects in the current selection?