At this point, it's kind of a given that Battlefield, or any game for that matter, will get additional downloadable content. DLC changes from game to game, but for Battlefield, as well as other first-person shooters, it usually consists of additional maps and possibly modes. We don't know what the future holds for Battlefield Hardline, but one thing is certain as of today: downloadable content can be expected.
Electronic Arts and Visceral Games teased today via the Battlefield Facebook page that new details regarding Battlefield Hardline Premium will be "coming soon." No other information was included but I think we're all smart enough to know what this entails.
EA's "Premium" subscription is basically the equivalent of a Season Pass. Battlefield 4's Premium subscription sold for $50 and included five themed digital expansion packs — Battlefield 4 China Rising, Battlefield 4 Second Assault, Battlefield 4 Naval Strike, Battlefield 4 Dragon's Teeth and Battlefield 4 Final Stand — and a slew of other perks, including two-weeks early access to all expansion packs, bonus Battlepacks, unique personalization options, and more.
In a recent roundtable discussion with lead multiplayer designer Thad Sasser, the top of future Hardline content was brought up. Although Sasser couldn't talk about any future plans, he did note that "everybody kind of already knows that the previous Battlefield has offered [additional] maps and modes and so on," suggesting that some sort of Premium subscription is on the table.
Now it's just a bit more official.