Blizzard has announced that it will be adding new heroes and maps to upcoming game Overwatch post-launch, and they're all going to be patched in for free.
In the video below game director Jeff Kaplan makes it clear that any additional heroes or maps introduced following the game's spring launch will not be sold as DLC. "We don’t have an exact timeline of when new heroes will be added to the game, how soon after launch, or how many," he said, "We just know that when we patch a new hero into the game, we want it to be free and not as DLC."
Given the competitve nature of the game, rolling out content to everyone rather than dividing the player base is a sensible move for the game's long-term viability.
It was recently announced that the game's beta will go offline next week but it'll be back in January.