This in conjunction with the AI allies and opponents
Well looks like Vince Zampella's Twitter is going to be the ongoing source for all Titanfall news. His latest reveal is that Titanfall will support a maximum of six players on each team, so 12 total real players. Vince added that this "turned out to be the best balance with AI for us." Remember, the maps are filled with AI allies and opponents as you're playing, so multiplayer matches do feel like a large scale endeavor.
It's a bit disappointing at first hearing the low player count, but based on my hands-on time with the game this may work out in the best interest for players. The maps are very open, and too many players could potentially make things too frustrating as enemies can literally come at you from any direction.