There's a point where your game starts to blur the lines between RPG and wargame, where players could command units of followers. That point intimidates people, for very sensible logistical reasons. Trying to keep track of any more than three followers in the theater of the mind becomes a nightmare. Foolish hubris drives me to devise a way to make it possible.
Once a player has four or more followers, have them become a Quantum Warband: a collective cloud of units that occupy a semi-large space in the theater of the mind, and are broken down into individuals only when absolutely necessary. Much as physicists cannot determine the exact positions of photons within space, so too we cannot determine the exact positions of your followers within the theater of the mind. You shouldn't need to!
Once you gain at least 4 followers (the number in which things start to become unmanageable), they become a warband. Track them on the quantum warband sheet: each follower is an entry on a table with as many entries as you have followers in the retinue. Record columns for HP, stats, and any special characteristics, items, or abilities. See the Quantum Warband sheet at the end of this post.
-If your warband is targeted by an attack, roll a die equal to the amount of followers in the warband to see who got hit.
-When a warband attacks, roll a die equal to the amount of followers in the retinue.
In the disorganized chaos of battle, that is how many followers get to make an attack this round. Make attack rolls (or just damage rolls if you're using ItO) for each of them. If they're attacking the same target, roll all attacks at once to save time (like warhammer).
-Warband AC is the average of your warband members' AC.
-Warband attack bonus is the average of your warband members' attack bonus.
-As long as at least one follower in a warband remains, the warband survives with all of its abstract (not items/equipment) experience and upgrades, as the survivor can train new recruits.
-At the end of each day that you do not give your warband some incentive (monetary, spiritual, pizza party, etc.), their current morale drops by 1. If you do give them an incentive, morale increases by 1.
-For morale checks, roll 2d6. If you roll lower than their current morale score, they pass. Otherwise, they may break and flee.
-The GM can call for a morale check whenever a warband drops by a die size, or if an enemy uses a fear effect, or if they are facing a particularly terrifying situation.
(for warband progression, we are using Spwack's Die Trying progression system, because it is very efficient, intuitive, and satisfying)
-In the spirit of Die Trying, players can put Xs on nearly any part of the warband sheet.
-spend XXXX next to your warband's name: it becomes more renowned, maximum number of members in the warband increases by a die size. Additionally, add a descriptor to your warband's name.
-spend XXX next to a member of the warband: that member becomes an officer or a specialist: they gain a special weapon or ability.
-spend XXXXX next to abilities: teach your warband a battle tactic, ability, or skill.
-spend XXXX next to morale: come up with a pithy or inspiring catchphrase, create a battle standard, or find some other way to increase cooperation and coherency: your warband's maximum morale increases by 1.
-spend XX next to any member of the unit: that member recruits a new member into the warband.
-spend X next to morale: break out the booze/pizza party/other forms of merriment: roll d6, increase your retinue's current morale by that amount.
This system is still a WIP and has some setbacks (for example, having to take average AC and attack bonus, which will be painful for certain very short periods of time, but will save a lot of drawn-out agony). I think overall it is a net gain. I am thinking more and more about the period of transition from RPG to domain-based play, and this fills a particular gap quite nicely.