As Naughty Dog says, all future maps and modes will be included with Uncharted 4 at no additional cost, and all vanity and gameplay in-game store items will be unlockable through gameplay.
Posted at the PlayStation blog, this article will get you prepared for the multiplayer part of the game by the time Uncharted 4 hits the stores, which is May 10.
Lastly, here’s Uncharted 4’s Multiplayer Roadmap: