I would be kind of sad if my favorite wild animals were passed over in favor of domestics, but a lot of people want them. The 3 biggest requests have always been birds, aquariums, and
farm/petting zoo animals, in that order. I have a soft spot for the Highland cow. I think a few other species would help the game feel more realistic.
Most of the domestic animals I've seen are in habitats without guests, but there are some (donkeys, alpacas, and especially goats) that are appropriate for guest interactions. They've added guest interactions with butterflies and stations, and I don't think it would be too much trouble to add a feeding and/or brushing mechanic for the guests to interact with these animals. I would propose a wider but lower walkthrough exhibit surrounded by a fence that could house a group of about a dozen of the following three species:
Alpacas,
Mediterranean Miniature Donkeys, and
African Dwarf Goats. Guests could walk on the path and feed, pet, or brush any of the three that approached them. They all should have decent color variation.
This pack would also feature barnyard scenery. (a tractor, hay bales, corn, other crops, possibly functional feed troughs) Hopefully some of it could add to the backstage props, which give so much life to the fancy builds.
This pack would also feature habitat animals. We could still use cows, pigs, sheep, and there are a few good choices for domestic birds.
Cows: At least 1 warm- and 1 cold-weather cow. At least 1 is essential.
- Highland cow: If we get any domestics, this is the main one that I would want. They are adorable and iconic for European representation.
- Warm weather cow: Watusi cattle and zebu also seem popular. At least one would make a good habitat animal. While the cooler/more temperate zoos tend to use the Highland cow, many of the warmer climate zoos will feature a different cow. There should be an option for both.
- Domestic Yak: another good choice
Pigs: One is enough and needed
- The Vietnamese Pot-Bellied Pig or Oceania's Kunekune are the obvious choices. I'd be happy with either.
Sheep: At least 1 would be good
- Valais Blacknose Sheep: Another adorable European floof and my backup pick if the highland cow is passed over.
- Cameroon Sheep: Another popular choice of sheep
- Priangan Sheep/Garut: An Asian sheep that could add regional variety if the other Asian domestics are skipped
Birds: At least 2, 4 if they start adding waterfowl
- Domestic Turkey: They are a larger bird and iconic for North America, which still doesn't yet have a bird. From Wikipedia, Toms are typically 13.5 kg, but the largest was 39. In comparison, the male peafowl is 4-6 kg. They would be a very different sized bird from anything else we have and they have a unique call. They also have a wild counterpart that could come in another pack. They have decent color variation.
- Helmeted Guineafowl: These are a commonly kept domestic and I've seen them roaming in several zoos in place of peafowl. They are somewhat popular and are another good choice of a bird. They are also a wild animal and could come in another pack.
- Domestic Chicken: I've seen them in plenty of zoos, but never as a walkthrough animal. They have a lot of color variation. They have a wild counterpart, the Red Junglefowl, which could also come in another pack.
- Waterfowl: Most of the ducks, geese, and swans I've seen in zoos were wild animals that could come in other packs. I would adore a Mute Swan. Also, the white Peking Duck or Chinese Goose could be cool.
Other:
- Lop Rabbits: If we get a rabbit, it might as well be a big domestic. I'm not convinced we need them, but the some would appreciate the rig.
- Guinea Pig: I truly believe they are too small to work as a habitat animal.
- Dromedary: I think it would work better as the backbone of a desert or Middle East pack later on.
While birds and fish would be cool, I think domestics would be the easiest to implement. I think each of the big 3 requests would draw in more players than a regular DLC, and deserves a slightly larger expansion pack with a few extra animals and scenery. I think they would need to add about 10-12 animals, excluding the fancy, new walkthrough exhibit, to properly address the desire for domestics. To compensate for the extra work, I could envision it costing up to twice as much, but more likely 50% more. I would enthusiastically buy this pack.
If I had to limit my choices to 4 habitat animals, I would pick the Highland Cow, Priangan Sheep, Kunekune, and Domestic Turkey to ensure all of the continents get something cool.