The next big step is the combat system, which we've just started working on. This missing feature will be a big update. This will involve a new animation system, a new VFX solution and a new game logic.
If we had designed the game for only one player, it would be much easier to develop, but because of the cooperative mode, we have to pay attention to many more aspects, as we did with the puzzle system.
New creatures and even missing Avatars are in the works, as well as a hand gesture system, not only for cooperative play, but also for spells and unique events. Then there's teleport control, which will be no small feat either. The rest of the plans will be worth talking about once we've passed these milestones ;)