So, I don'r think we have anything about arc 4, (correct me if I'm wrong),
about arc 5 we have learned that Darkstar and Ghostfreak return, and also that there is a Zombozo episode which they recorded on Halloween and
about arc 6 we know that ChamAlien may appear.
Also, Matt Wayne confirmed that they are working on an arc which invovles the Plutonian Revolt, that I bet is either 6 or 7 as Derrick said that they likely have more than 60 episodes.
So, post your thoughts and other information you can remember about the next arcs/