Don't know if it has been brought up before but have you thought of any sort of implementation of Morale? Morale has always played a huge part of winning and losing battles. Simple implementations of morale systems can really unify a team or break an army. This encourages players to band together, using each class to their strengths. Players will be encouraged to form Battle Lines (feeding into community run regiments). This would also steer people away from the "Lone Wolf" mentality because they aren't getting any bonuses and will likely face an enemy receiving combat bonuses.
One of the ways that this system could be implemented would be to assign base morale values for each class and bonuses for being in proximity of other related classes.
//A rough idea for some classes - Just for morale (aura) bonuses//
Class - Bonus Aura Radius - Effects -
Officer - 15m - Reload (3%)
Line - 5m - Melee Attack Speed (3%)
Light - 7m - Accuracy (+2%)
Rifle - 6m - Damage falloff (-10%)
Carp - 15m - Structure Damage (+10%)
Surg - 7m - Health (+10%)
Fife - 15m - Accuracy (+5%)
Drum - 15m - Accuracy (+5%)
What does it all mean?
This system can be very dynamic and customized to whatever you want it to do. This could mean that only other Line Infantry can receive your bonus is you want that or only riflemen and light infantry share bonuses. The world is yours.
What happens when someone dies next to you? -The Meat and Potatos-
Each player will keep track of variables that track the number, rate of death & type of players dying near you. In turn, the player will suffer a penalty based off of these variables. The easiest thing would be to make the penalty the inverse of the bonuses that class provides.
Imagine you find yourself in a large group of 20 Line Infantry, Officers and Musicians. While these support classes (officer/musicians) are alive, all players receive the bonuses they provide. Say, your line takes a volley and only loses 1 Line Infantryman. Every player within that bonus aura will now receive a small penalty for a very short amount of time. Now, say you take a volley and it kills 20% of the soldiers, officers and musicians in your proximity. Players receive a substantial penalty to (as mentioned in the table above) to their Reload speed, Melee Attack speed and Accuracy for a much longer time.
After your line has sustained very visible casualties, the enemy line can take advantage of this (still enjoying their bonuses) and obliterate the remainder of your line with far more ease than they would have been able to before.
How can this be implemented?
You already have the vast majority of the system built. Musicians/Flag bearers already grant players within their range a bonus. The positive bonuses can easily be applied to every class with only a few lines of code. Tracking living players within that vicinity may be slightly harder, but can in all honestly probably be done with A) Colliders B) Ray Cast C) Line Cast and a new class.
Some amazing games out there use boring morale mechanics but because each soldier is controlled by a human in Holdfast, you can take a much deeper approach into team play. Games like Squad, CS: GO, Heroes of the Storm and countless others require team play. This brings the community together, allows new players to pick up the game faster and for players to focus on helping their teams rather than trying to lone wolf it for nothing.
I appreciate you guys reading this and hope you like my idea.
Certainly an interesting idea, though I'm unconvinced that players would enjoy being put at a disadvantage via coded de-buffs rather than pure skill. I prefer the naturally emerging tactics and strategy currently present within the simulation, and I shall provide an example so that you may better understand my meaning.
Say that a friendly line of infantry is flanked heavily from the rear, and takes heavy casualties; they have already been de-buffed in literal morale and physical strength by the slaughter of their fellow man; therefore, they retreat, and potentially grant themselves enough room to regroup and press a renewed attack. The tactics are used successfully by the enemy to destroy the friendly ranks, but the friendlies are de-buffed through action and mental processes rather than a passive de-buff mechanic. As such it is more fluid, and more fair, as the only thing separating the friendly line from victory or defeat is their own skill, rather than whether a passive de-buff manages to be inflicted upon them and hamper them to the point of utter annoyance.
Perhaps I am mistaken, and a coded de-buff of morale/accuracy/speed will promote more careful tactics all around, it won't become merely an obnoxious hazard to the player base, and it will most certainly add that apparently all-important realism some crave, despite natural occurrences creating realism (Run away, they just killed 15 of our 20 men!) through active player interaction. I do not believe that to be the case however.
Understand that combat provides its own stimuli that drastically affect player decision making on its own, and that de-buffs only harm a game, no matter what form they take.