Unlocking control of a single troop, and you have to move them manually using the arrow keys. You'd lose control of everything else.
That would be a AAA Easter Egg. A CA's Total War control over a turret/cannon.
Yeah, this is something I've kicked around in my head. It would be kinda cool, though you'd probably notice just how bad the crew animations really are.
Now the really "never gonna happen but cool" version of this would be multiplayer: each crew member is controlled by a different player. It's like Guns of Icarus, but with most players stuck with needing to ferry coal back and forth or do "press X to keep suspendium chamber running".
Yes.... Splendid! Maybe add control of guns for random, green-and-shooty based shenanigans...