So there's a lot of species in the game that have been backfilled to the older maps after being included on newer maps. However, there's still quite a few more backfilling options. Here I'll give a list of species that could be backfilled onto existing maps and which maps they can be backfilled to. Not all these backfillings need to happen, but they would help to make each of those maps more interesting and varied in terms of wildlife you can encounter there and would give us more maps to hunt these species.
Black Bear (Yukon Valley)
Black Grouse (Medved Taiga)
Bobcat (Silver Ridge Peaks and Mississippi Acres)
Canada Goose (New England Mountains)
Cinnamon Teal (Silver Ridge Peaks)
Coyote (Silver Ridge Peaks)
Eurasian Teal (Hirschfelden)
European Mouflon (Hirschfelden, renamed Iberian Mouflon)
European Rabbit (Cuatro Colinas and Emerald Coast)
Fallow Deer (Parque Fernando, Cuatro Colinas and maybe Vurhonga Savanna)
Gray Fox (Rancho Del Arroyo)
Green-Winged Teal (Layton Lake)
Hazel Grouse (Medved Taiga)
Mallard (Mississippi Acres)
Mountain Goat (Layton Lake)
Mountain Lion (Layton Lake)
Red Fox (Layton Lake and Silver Ridge Peaks)
Ring-Necked Pheasant (Silver Ridge Peaks)
Roe Deer (Revontuli Coast)
Tufted Duck (Hirschfelden)
Water Buffalo (Emerald Coast)
Western Capercaillie (Hirschfelden)
White-Tailed Jackrabbit (Silver Ridge Peaks)
Wild Boar (Parque Fernando)
Willow Ptarmigan (Yukon Valley)
Let me know which of these you would like to see in the game.