It's certainly a unique idea and I definitely like the thematics of it. I'm not sure how I'd feel about it as a permanent upgrade though. It would work but it does change the dynamics of the set somewhat relative to the other MM sets which could be a good thing or a bad thing. It also adds a very strong incentive to keep pets alive that isn't in the other sets which, again, could be good or bad. Additionally for the graphics changes the SCR applies.
I think it would be an easier sell if the bonus was larger but applied for a limited time instead of the remaining life of the pet.
In terms of the specific implementation you're proposed the only one I don't like is the Soldier. From an implementation point of view the other changes could be handled similar to Dual Pistols (when you use the power it checks for certain buffs on the character and adjusts the power as appropriate). However for the soldiers the base type of the power would be changing (from single target to cone) which would be a lot more problematic to implement (I'm not going to say it's impossible, but it would definitely be problematic).
So instead, how about making the Armor Piercing Rounds give a -resistance debuff and giving them to the Spec Ops instead (Soldiers get Cryo Rounds). That would give the group as a whole a nice damage buff against single targets.
When I first posted this thread, it was in the wrong section of the forums so I'm reposting it now.
The power essentially functions as a T1.5 equip henchman. It is a single target upgrade on a two minute timer (can be reduced). It adds a minor 7% extra lethal and smashing resistance (the visual effect is a pair of sholder pads on all types of henchmen similar to the ones on Malta Tac Ops.) and a new gun.So after browsing the Improving Mercenaries thread (http://boards.cityofheroes.com/showthread.php?t=183743) I looked at some of the ideas being tossed around. The one that struck me the most was the idea of using DP's ammo change as a replacement to that god awful power Serum. I can't remember who made the original suggestion (whoever did feel free to chime in), but I thought I would refine the idea a little bit.
The Power
Ammo Upgrade - Ranged, Enhance Mercenary Henchmen
Soldiers - All Soldier burst attacks (excluding full auto for obvious reasons) can hit one extra target, functioning like Piercing Rounds. The soldiers gain a Council Assault Rifle as their weapon.
Medic - the Medic gains chemical rounds that change his burst and heavy burst to 80 Lethal/20 Toxic. the Rounds have a chance to lower the enemy's damage. The medic gains the modified CAR that SWAT Equalizers have.
Spec Ops - Spec Ops snipe, burst, and heavy burst all become 80/20 lethal and cold. The attacks have the regular cold debuff associated with cryo ammo. Spec Ops gain the sniper rifle version of the CAR (you can see it on display in the Quartermaster's counter in the DPO).
Commando - Burst, Full Auto, and Slug now deal 75/25 lethal and fire and have a chance to set the enemy on fire. The commando's weapon stays the same since I couldn't find an existing gun similar to it in game to use.
Overall
This change would allow mercenaries to be a much more flexible powerset and focus on quality over quantity. Giving a third upgrade power helps the powerset to be unique compared to other powersets.
The reasoning for the low secondary damage numbers is that Mercs is a lethal set, I wanted to keep the powerset focused on that with the secondary damage types making up for the fact lethal damage is on of the most heavily resisted damage types in the game. The reason behind the two minute timer and single target upgrade is to force the player to choose what damage types and debuffs they need the most. It keeps the ability from being used to instantly equip your entire squad with powerful debuffs. That being said, you CAN equip the entire squad and if you play your build right, say lots of recharge reduction + Hasten, you could equip the squad fairly quickly.
The extra smashing/lethal protection gives your merc pets a little more protection, since they tend to be a bit squishy (at least from what I've seen).