The developers behind the latest XCOM title recently told Polygon that they have more DLC coming to the game. Jake Solomon, the lead designer, said that the previously released Slingshot and Second Wave add-ons weren’t all they had planned after all.
“We do have more content coming in 2013. We’re working on something really awesome.”
Whilst Solomon wouldn’t reveal any more details, he did say that it’s “going to take some time” in order for the studio to finish work on the new content. Speculating on that; perhaps they’re looking at releasing a much larger add-on than the limited Slingshot DLC. I personally think that it’s going to be a full blown expansion, ramping up the difficulty in some new way, maybe incorporating some themes of the older XCOM titles into it.