Titanfall game mode additions will be available to everyone according to a Tweet by Vince Zampella in response to a player.
@YaBoyZD3 Modes we release will be free to all, not part of DLC.
— Vince Zampella (@VinceZampella) March 25, 2014
Usually, game modes appear in online titles as part of a DLC which fractures the community to those who own DLC and those who don’t.
We know there are four DLC’s planned for Titanfall and a Season Pass gets you all of them with the ability to purchase them individually. Zampella has also confirmed that the game’s first DLC is already “in the works,” but added that it is not quite done, and doesn’t have an official release date. He confirmed that it would be included in the Season Pass, or be sold separately for $10.
So what will DLC contain if the game modes will be released via free updates? Probably weapons, maps, campaign story line and possibly new Titan’s. Usually the system involves everyone getting the content so all players can play the standard maps together without splitting the community based on what weapon they pick to use.