What about Unruly being this way:
Units with one or more model parts having Unruly, suffer a Discipline modifier of -X in all tests of Redirect Charge, March, Restain Pursuit and Combat Reform. If the unit contains models with different X, only count the largest.
Feral Orcs: Unruly 2
Normal Orcs: Unruly 1
Iron Orcs: ---
All kinds of Goblins: Unruly 1
Trolls: Unruly 4 (but stubborn, no stupidity and Dis 6)
As it's own ability we are looking at something which would have a benefit for preventing a Break test, and bad for anything else.
What does the army gain from this? Better OnG feel? (A: Yes)
Better at Grinding? (A: Yes)
Will it be fun for OnG players and opponents? (Profit!)
Is there another fun way to have similar effect? (Yes)
So I think the last few rules suggestions made are all solid, and would be used in conjunction if we changed direction. I would go with this.
Units comprised of one or more models with this rule and not joined by a model with the Front Rank rule are effected as follows:
Break rolls by the unit are subject to Minimized Roll.
All other Discipline tests are subject to Maximized Roll.
We eliminate the Unruly Horde formation rule, and go back to the old "Bring the Pain"