How about simply changing skins for Allies when they end up with US/Russian armies mixed ? Just like America's Army, where you always see yourself and your teammates as "the good guys", Russian players could see their US allies with Russian skin, and vice-versa for the US players. You know, something like T34 <=> Sherman, US Riflemen <=> Conscripts, etc..., only skin and speech accent could be affected.
I like the idea, would simply be soviet leand lease comander. Rifle men could be strelki with M1 Garnads getting replaced with Svt-40's and bazookas being simply lend lease bazookas. Without stat changes. Same could be done with maps Semoski getting some of its building replaced to look like Semois.
Tho it would be alot of work, so its probably not going to happen. So the only option will be US Army + Red army vs Ostheer + Westheer. Or they go 2 US vs 2 Westheer, and 2 Soviet vs 2 Ostheer, since 2 Soviet or 2 US-Army vs Ostheer + Westheer would cause a lot of complains.
Imo it would have been better if they would have just added one new faction the US-Army. And kept a new Wehrmacht fraction for a next expansion. Btw OK West should be renamed to Army Group West or Westheer imo.