I thought I'd give the war coordination feature another try in this last campaign. It had been long enough (1k + hours since) and I'd grown as a player. Figured either I could find a way to utilize it better now, or it may have been updated.
And honestly it's still relegated to the feature graveyard as far as I'm concerned, along with vassals.
I'll give a good example from my game.
My military allies had been mostly cheering me on and sitting out of the war we were in, but I happened to notice that they had an army not far from an enemy settlement. I thought it would be fun to fight a battle with some allied friends, so set a war coordination target for the enemy settlement, and start besieging it with my army. Could've fought it myself on that turn, but it sounded fun to take it together.
Well.. 6 turns pass and eventually my enemies bring reinforcements and I do the smart thing and back off (I guess sacking would've worked but I wanted to see what my allies would do). And what do they do? Charge "bravely" into all 3 armies the turn after I leave and get massacred. -.- Woo, great work guys! /s
So as far as I'm concerned the feature is pointless right now, and that's a bummer for new players trying things out, and old players. But there's always hope, it would be cool if war coordination wasn't useless. Which is harsh to say, but it's true right now.