i know vol. 5 came out before a lot of things happened in the comic but like, are the alpha kids allowed? what about depictions of things that happened near the end of the comic? how much should we keep the artistic focus on the earlier days of homestuck... if at all?

Basically, we are saying go with what you feel is most appropriate! Many songs (such as Can Town or Vertical Movement) are more clearly dedicated to a single character/scene, so the artists are more likely to draw those. On the other hand, songs like Homestuck Anthem were flat out used in aplha scenes, so those could use alphas on the cover. Others like Light or Sarabande are more up in the air with their meaning (seeing as we werent able to get answers from all the musicians about their music), so those, as long as they can explain why they feel it should be a certain design, can go with whatever.