The website Cultured Vultures has release a short preview about Elex. In it, the editor describes the setting of the game and compares it to Bioshock. She concludes her impression as follows:

Put simply, ELEX is an auspicious sci-fi RPG from an experienced studio set in a stunning – and seamless – open world full of characters, creatures, and quests.

Furthermore the preview is mentioning that Elex won't get any paid DLC, but only a free expansion or a proper sequel, if any. Since the preview has been shared by Piranha Bytes and the official Elex page on Facebook, it's safe to assume the information is correct.

Good news for those who aren’t a fan of shelling out lots of money for additional content: ELEX will not have any paid DLC. Any additional content will arrive in the form of a free add-on, or even a sequel, although there are no plans for one on the horizon just yet.