By adding the ability to have mirror matches and same team fights, you add so much more playability to the game.
People will download your mod in droves.
The only valid arguments for not having it are,
1. Balance Concerns
Who cares about balance for USSR vs Allies, if anyone complains, tell them that you are not balancing it. Same with Mirror matches, they are balanced anyway.
Seriously, think about this.
If you allow mirror matches and allies vs allies and axis vs axis, you will get tens of thousands of new downloads and they will also play the main EF game type meaning more normal automatches so it's a win win for everyone!
2. It's not realistic
It's a fun game, COH is so unrealistic its not funny atm. Don't stop something which would be fun because it's not realistic in an unrealistic game.
3. It ruins automatch
Just stop automatch from allowing these types of matches, custom means custom. Why should you dictate that you should only play these matches, let the gamer choose. If they think it's stupid then don't play it, again, Win Win
SERIOUSLY, PLEASE THINK ABOUT IT!!!!!!!!!!!!!!!!!!!