Your trick with opening the inventory and pressing the back button doesn't work because I don't select and control my units in descending order.
Why does this matter? You can still find the 'lost' fellow, even if it takes more clicks and maybe some examination of TUs to find the right person.
Or, in other words, it's a question of
some inconvenience vs implementing
and maintaining a wholly new functionality.
I also use the 'skip' function a lot (mapped it to spacebar due to 4X habits
), and it's relatively rare that I have to find a skipped guy who hasn't moved yet. And if I do have to look for such a soldier, it's because he wasn't particularly important to the battle, otherwise I'd have manually selected and moved/acted in the first place.