Actually, somebody made a beta halo mod already, but its for swbf 1. He may make it avaliable for swbf2 as well, but dont hold your breath. As for the civil war mod, it would probably be the hardest to make, because you'd have to alter the ai to walk in rows into enemy fire. that is, if you want it to be historically accurate.
I doubt he'd even try making them walk in lines... ALL of them would be hard.