Secretary bird, marabou stork, japanese crane, shoebill, emu, southern cassowary, white stork, black stork, grey crowned crane, brown pelican, pink pelican. THose are possible to make without programming flying.
I think the most likely would be the emu, I can't imagine an Australian Pack without them, plus they would be really easy to make using the existing ostrich rig. When it comes to what I would like... probably a pheasant, as the "European version" of the peacock. Scarlet ibis would go nicely with flamingo, even better if they enrich each other.
All pheasants have a native range from Asia But it's true they are very present in Europe even outside zoos, a golden pheasant or something like that woul be useful.
Now talking about European version of the peacock, a capercaillie woul be cool. Gorgeous guys:
Prairie chickens could be an American version of the pheasant, but I don't know how common are in zoos. And helmeted guineafowls would fit in almost any African herbivores enclosure.
And following the example of the flamingo, you have a wide range of ibises, spoonbills, herons, storks... But I think that very probably the most useful waterfowl for any zoo is the mallard. Give us ducks!
All pheasants have a native range from Asia But it's true they are very present in Europe even outside zoos, a golden pheasant or something like that woul be useful.