I feel like it's likely it's North America related. I figure the Moose and Cougar/Mountain Lion are very likely to be included (I can't see how the latter can be left out, honestly). A mix of Sea Lions, American Beavers, American Alligators is also likely. Less likely but still high profile, Arctic Fox, American Black Bear, Wolverine and Prairie Dog. I don't think we'll get all of these of course, just the list I'm thinking they may be pulling from.
If it's not something specifically North American, I'm thinking it's got to be either Europe or some biome or collection that gets the Capybara in. Frontier knows it's highly desired. I feel like Europe is third most likely, with some kind of jungle/forest/rainforest pack as the second most likely release. That could also get us another otter, Red River Hog, Gibbon, Tasmanian Devil, Wombat...the list goes on and on. But I think it would be more logical to get North America done first, unless the Cougar and Moose were to show up first in that kind of pack.