DICE have confirmed that any future content that they release for Battlefield 4 - including all the things they've already announced - will be free for all players, regardless of whether or not they own a Premium pass.
In the works at DICE are night versions of several maps - including Siege of Shanghai, Zavod 311, and Golmud Railway - as well as a new community map that has just gone into development. An unannounced map from an earlier Battlefield title is also on the cards, and details will be confirmed in the future.
A new game mode - entitled "Gunmaster" - is on the cards too. That's coming in the next patch (release date as yet unknown) and will bring with it five new weapons in the form of the AN-94, Groza-1, Groza-2, and L86A1 assault rifles, and a compact rifle known as the Mare's Leg.
It should also be noted that Battlefield 4 is free for EA Access subscribers, as the game appears in the service's Vault on Xbox One.