Played warcraft a bit for nostalgia's sake and noticed the share control function.
Basically, you check the box next to a player's name and that ally can control your units too. A notification pops up to tell them, of course.
This works one way, he has to share back to you for it to become two way.
ZK should have that. And have a function where someone who has been granted control can revoke it on his side. (so it doesn't clog up drag select)
Note that this is different from sharing a team number. You still count as two players, you do everything as if you were independent, just that he can select your units as well.
This lets players who can trust each other (eg. clans) micro each other's defences during some spare time or move an annoying blocking unit or make an idle builder drop some cheap eco or... etc.
Might need to show allied selections though.