Actually no, maybe depends on the type of player. The example (the combinations) you provided does not show any improvement on that part, imo really needs to be more unique than that.
Would be nice to have 2 more but will this make much difference on how long the "hype" will stick with me or on this forum? Definately not.
I think new game mechanics/building options/features have more impact for me and i've seen some other players comment similar things.
I'll be honest, I'm not entirely sure what you mean by "needs to be more unique than that". We already have semi-aquatic animals that can dive now, so the only two things that I can think of would be
-Aviaries
-Aquariums in some fashion
Aviaries I think will happen at some point, hopefully by the end of the year. Aquariums, unless it's basically just the same as a small exhibit, I don't see happening at all. As far as new game mechanics are concerned, those are always free in the base updates. Diving was implemented to the Saltwater croc for free, and they've said other base game animals will be updated in the future.
I think the best way to keep people involved is by making sure each pack as a good representation of biodiversity from whatever location it represents, more of it (again, at least 6 habitat animals going forward) and making an effort to have animals from different biomes. For instance, if they made an African dlc pack, it would be far more fun if it had:
-A black or white rhino (Grasslands)
-Meerkat (Scrub/desert)
-Cape penguin (Coastal aquatic)
-Serval or Caracal (Scrub/Grasslands)
-Hamadryas baboon (Desert/Taiga)
-Red river hog (Tropical rainforest)
That would be much better than having a pack with four mammals that are all from the grasslands. They almost got it right with the South America pack (excluding that it had far too few total animals), it's just that the llama was, frankly, a terrible choice.
Edit: I also just want to say, you mentioned new building pieces as a way to keep people interested. I don't think that works at all. We got far more new scenery pieces in all four dlcs than animals, and even people coming from PC who are primarily builders have said they'd rather see more animals than scenery. I'm quite frankly sick of hundreds of new building pieces. Most zoos don't have every single section of their zoo themed around whatever country/continent those animals are from.