Some things that I need to point out.
And I'll use this example, based on the State Troop Detachment
W=Swordsman, S=Spearman, H=Halberdier, X=Crossbowman, G=General, O=Outrider
WWHHHHHHHHHHHHWW
WWSSSSSSSSSSSSSWW
WWSSSSSSSSSSSSSWW
WWSSSSSSSSSSSSSWW
WWXXXXXXXXXXXXXWW
WWXXXXXXGXXXXXXWW
WWWWWWWWWWWWW
OOOOO
Halberdiers facing the enemy, crossbows just behind the rear
This is 6 different units, even if it's only 4 differnt Warscrolls. Each unit must maintain unit coherency of an inch, and if it moves in the movement phase, it must move together if it has lost coherency. Though it doesn't have to actually move, just tht if it does it then has to join up.
As each unit would make a separate roll for a run move, to move this quickly as a block, it's moving at the lowest of all the movement.
Each unit would have to make a charge attempt separately, and here is where the formation becomes a problem. A unit can't move to withing 3" of an enemy. When it charges, it must get to within half an inch in order to complete the charge, or it doesn't move at all. Even with 20mm square bases, they are more than half an inch wide, you have to hope youe enemy unit has parts of a model sticking out far enough (Though we also have spears in the formation, so that helps...but even so, it's scope for arguments about wether it's completed a charge or not.
So, this formation coudn't really charge as it is, though it could recieve a charge, which is often a disadvantage.
In the combat phase, even those likely to be able to pile in, or have the weapon range to attack, you have 3 or 4 units to activate, against maybe only one for the enemy.
This formation is deep enoough to keep the xbows out of combat for a while, which would mean being more than 3" from an enemy. However, given that the have two units of the same height as them, they wouldnt' be able to see much, unless anything the could shoot as was taller than a man sized, as though the second rank of xbows can see through it's own unit, it can't see through the spearmen or halberdiers. The outriders, sitting higher up, and can therefore see over the unit could still shoot though
Also with piling in, I've seen many times that people pile in anywhere they want, and that's not how it works, the pile in allows you to move toward s the closest enemy model. Though not necessarily in a straight line, as it doesn't specifiy that. Using pile in to get a mix of two units in, isn't going to be as straightforward as you might thik. And Models can't be moved over other models, unless they can fly.
I'm not trying to dismiss the idea of formations, just pointing out there are limitations within the rules to consider, when coming up with them
