i was thinking of a combiner drive which would link all units in the team to a core unit. The movement of all tied to the core unit. The bonuses of the combination would depend on the units and the form chosen. The form chosen could be dependent on a template loaded into the combiner drive. The combiner drive would most likely be a leg slot item which would increase the mass of a unit by a certain amount and only be active for a short while.
possible forms:
   Bunker: No movement, reduced recharge time, Bonus to Armor
   Turtle: slight movement, lesser bonuses to recharge time & armor than bunker
   Giant Biped: Bonus to weapon, targeting, and signal detection ranges

I also thought being restricted to player teams might be a problem. I thought perhaps the use of subordinate units whose abilities are penalized due to multitasking drawbacks. Targeting would alos be limited to primary targets and not be able to switch ammo types once launched. From what i've seen the npc drones stay relatively close to thier spawn point, could the spawn point be changed to the owner PC? the spawn rate would need to be disabled. The Subordinate Link would likely be a head slot item which would heavily penalize all skill levels.