I like the Idea of this, it'd be cool to see some American OPFOR units...
Also, some infantry using parts of U.S. Millitary equipment (never a whole set, just patch-work stuff they could have stolen or salvaged) would look really good... you could modify the HYK Modern U.S. Soldiers pack to get that effect (with permision, of course). Just stuff like ressistance fighters wearing U.S. Helmets, body armor, etc, and using M-16s and the like would look really good.