I think the pattern for costume variants would be stuff that both distinct from the already existing versions and is outfits that would be unlikely to be included in a set. Like even if they make a Ministry or Magic escape I don't think they'll include Dolores, and even if they do a Hogsmeade I don't think they'll include Minerva. Thinking about it Igor Karkaroff probably has a good chance of being included in the new CMF. He wasn't in the last wave so it seems like it would make sense to include him now so people can add him to the Yule Ball, kinda fill out the cast a bit. Also all of these people would need new head gear molds so it makes sense to have them in the CMF.