I could see this work since it basically is the combat part of the game, but where you can control aliens and soldiers in the same team against a friend. Not like Mass Effect 3 (trying to make it effect single player but more of just a grind for some pool to fill for a "better" ending) or Bioshock 2 (kinda felt forced, multiplayer can keep the community interested in your game so developers are forced to do it.All the soldier types are available, but you can pay more for more powerful archetypes and items, such as medkits and combat stims. So you can, if you wish, pimp out a solider with Titan armour, a medkit and a snazzy plasma rifle, but you'll have spent half your budget on him in the process.
On the battlefield, what strikes you first is how odd it is seeing soldiers and aliens in the same squad. Everything about the XCOM single-player tells us to hate the aliens, to fear them, to destroy them. When a Berserker bursts out of the fog of war it terrifies you. Now, I've got a Berserker watching my assault soldier's back.