The Hive God 'Nokris' is almost certain to turn up in a few years, just seems well placed to have his statue next to Oryx's and Crota's in the Regicide mission. Im unsure about the rest, but I'm confident in saying the DLC's 3 and 4 will be based around Osiris and the Cabal Empire itself. Theres way too many hints in the Grimoire (especially about Osiris), and in game too for them to not be a major part of each DLC.