Shared control of assigned units

As the population cap may get higher -cause, zoom is allowed and so maps get enlarged- army management requires to create units for quick access. What would be innovative is to give control of a specific group of you military or even workers to a specific ally, in order to secure a zone or make a joint attack while you’re busy in another front or matters. Say, select a group of 2 workers and 12 cavalry near to you next-to-be town centre and your buddy is interested in you settling there as it is the entrance to his dominion, then you allow him to control those units, build the town centre, and even get a tower in there.

It’s a very innovative idea indeed. But it also sounds like the 2player controlling 1player option, which is already possible in multiplayer (if you select the same team at the start).
Being two different entities though, I don’t know what to think of it.

Like: Does the player who’s units are being allied controlled have to give permission for it?
Because especially with building stuff (from your stockpile) it can be a pain if your ally does it wrong.