What do mean "turn unit"?

it mean the ability to point a ship in a specified direction without actually moving.(thanks Arseface)
don't move forward.

Yes, this would be very useful (assuming you mean the ability to point a ship in a specified direction without actually moving).

There are plenty of times where I have cap ships in battle, and I want to point them all in the same direction ready to leave at the same time, or ensure they all take the same path to the next planet.

Yes please. If they can do it on their own in combat no reason they shouldn't be able to on demand.

I think that at present, it is simply wistful thinking to assume it will come out in Sins or an expansion for base Sins. It would require what I imagine to be a great deal of new engine coding.

That, and the fact that it would simply be better to MAYBE release a new full-on expansion for Sins, and then move on to something else. What that something else might be, we simply don't know.

At present, IC has 3 options with Sins once Diplo is released. A new full-out XPack, a sequel (this is where you would probably get a turn unit control, preferably on all 3 axis (6 degrees of freedom baby!) or a new franchise to let Sins age a little.

EDIT: stupid action on my part, forgot to add that I would like to see such a control. It would be IMMENSELY useful, especially for microing fleets and likely useful for modders.

YEAH!!!!  I would love it, even if it was just on cap ships!!! 

I would also like better directional control of moving formations... maybe different formations themselves.

Agreed. I hate it when your cap makes this wide, sweeping path and then runs into a mines or worse: the enemy fleet.

At the present moment, we actually have this functionality in the game, albeit in an improvised manner. Simply order your ship towards the direction you want it facing and immediately order it to stop. At worst, the ship will move about two units forward, but in just about every case, it will turn towards that direction after stopping. Or just turn, considering it might not even move when you attempt this.

With how simple this method is and how effective it is, I really doubt that the engine would need any new coding. And if it did, most likely an almost trivial amount.

Of course, I'm all in favor of having this added in. What I'd like to see is an implementation like the one in Dawn of War II; holding your mouse button down on empty space allows you to order the selected unit(s) to face in a certain direction when they arrive by dragging your mouse around.

I'd like a "Turn Unit(s)" command.

I would agree. A simple key+mouse combination to turn the unit in a specific direction but not move.

It could be as easy as selecting the units, then pressing and holding a user-specified key and clicking the direction you want the units to face.