So far, Europe and Madagascar got anniversary animals. Oceania and Africa just got their own packs, and Asia had some decent rep in the spring pack. I think the next one, if we get one, is likely to be from NA or SA, maybe Asia?
NA has a few icons that would not require much effort. As much as I want the ABB, I'd be surprised if it were an anniversary animal because I think the color morphs could be used to help sell a pack. A lot of packs recently include at least one animal with a bunch of color morphs (Dromedary, Lar Gibbon, Red Fox, Fallow deer). Even the blue penguin and kiwi came with a few. I do think it will turn up in some kind of temperate pack, hopefully with some NA scenery. I really want cabins/camping as well as something for at least one of the Native American communities. It's a little odd that there's nothing yet.
SA desperately needs to catch up to other continents. The lack of base game SA primates seems like the most glaring omission in my eyes. They are so popular in zoos worldwide! There are also some great options for SA birds. I think something from SA is most likely, unless the winter pack will be neotropical animals. In that case, I could see them adding a takin or something so people don't get too upset about the lack of goats. Maybe a blackbuck because people were also talking about Indian rep? A SA animal, especially a monkey, would make the most sense for an anniversary gift. As much as I hope for tamarins, I think it would be something lower effort, like the squirrel monkey. It's not an exact clone to the capuchin, but it seems pretty close.