A Respawn guy commented in the GAF forums about the 6v6 decision:
Lots of armchair game designing going on in here. I'd suggest playing before judging a something as insignificant as a number in a vacuum.
Vince is right - we tried a huge amount of playercounts (all the way down to 1v1 and up quite high) and designed the maps, gameplay mechanics, and entire experience around which played best. If anyone wants to chase the numbers game, perhaps we're not the experience they're after? I dunno.
And FYI, for amount of stuff happening at once in a map you'll be hard pressed to find a game that keeps the action higher. I literally have to stop playing every few rounds because my heart just can't take it some times. Remember, you can get out of your Titan and let it roam on AI mode - meaning there can be 12 Pilots wallrunning around, 12 Titans stomping below, and dozens of AI doing their thing.
Oh, and I keep seeing people thinking we've got "bots" when we talk about AI. Thats not how they are. The AI in Titanfall are not replacements for human players. Our playercount is not 6v6 because of AI - AI play their own role in the game and are a different class of character in the game.
Can't wait! Only a couple months until speculative threads like this are gone and people are actually talking about their experiences with the game. Its truly fun stuff, and I hope everyone at least gives it a try.
I'm not too worried, can't wait to play it.