I fail to see the problem. Yes, I'd have to move back 5 times instead of 1, but how often does this happen? Once per 10 hours of playing? And even if that's the case, what's so hard about this?
Again.
EIGHTY. FIVE. SOLDIERS. It's not "1-5 clicks" for me, it's 1-84 clicks looking for a specific soldier with no identifying marks who is indistinguishable from other soldiers with full TUs who have not moved yet, and soldiers with full TUs who were previously hidden for reaction fire purposes. Not a problem on small scales, but a big problem for me because I deal with this on a regular basis.
Enemies attempt to invade my bases multiple times every month, sometimes twice in the same week, and every time that happens I have to control as many as 85 different soldiers, not including any assorted HWPs and war beasts. When sending soldiers to a particularly dangerous mission I often deploy as many as 24. In order to keep up with the daily threats I face I require dozens and dozens of soldiers because missions come fast and often, while wounds and combat fatigue force me to cycle them out after every deployment. This wasn't by choice, this is just how XPiratez is in the midgame.
For "prev" unit, if behavior would be "go to last ignored unit (if was any)" then this could be implemented too relativity easy, as we should only store
one value for last unit (question is if should be remember after save/load?).
Only if it were very easy to add that value to battlescape save files. Otherwise simply keeping it in memory should suffice. The undo button is an "oops" feature that players will use immediately to correct their mistake, or not at all.