The best thing about the next DLC is that, unlike the previous ones, this time it's completley unpredictable. In my mind there are three possible options:
-European DLC. Would be the least exciting maybe, but would make a lot of sense, given how Europe's fauna is underrepresented right now. I just hope that if it's an European DLC it'll bring more than the usual 4 habitat animals and/or a new game mechanic.
-Aquatic DLC. The leaks and some other hints really make this one the most likely to happen. However, I think there's a chance we'll get this later in time so they completely polish diving mechanics.
-Generic Zoo pack. Doesn't sound super exciting, honestly, but if done right could be the best option of the three. It could add some of the most missing animals (African rhino, meerkats, red deer, alpine ibex, etc.) and some requested features or pieces such as the mesh pieces, backstage props/pieces, animal gates, vista points, more variation on exhibits, etc.