This is an even bigger challenge than the 30 animals left in the game list. However it does take all the pressure off, since you are asking for the top 10 must have animals, and there could be a 100 more after that, so I think I can do it.
1. Leopard (either African/Indian/Indochinese, it is the last majestic big cat missing in this game)
2. Lar Gibbon (This is definitely a must have, it would just add another element to the game if brachiating animations are finally developed, without them then this animal should stay out of the game, we do not need a second Orangutan)
3. Marabu Stork (This might seem like a random choice but it is definitely everything but. We seriously lack birds in this game, and Marabu Storks would behave in similar fashion to the flamingos in game. They would be a much needed avian addition to African Savannah, males and females are quite distinct and they mix well with other species. I have often seen several players ask for Secretary Birds, not sure if this is Zoo Tycoon thing, but those birds would be extremely limited as far as mixed species exhibits.)
4. Sea Lion (When the aquatic DLC was released this would have been my number one pick to be included, it was surprise when they were not, probably saved by Frontier for the North American DLC)
5. Great White Pelican (Not my favorite choice of Pelican, the Brown Pelican or Peruvian Pelican seem a little more interesting to me in color and variation, however since the game has African flamingoes it would only make sense to get Great White Pelicans, so we can finally have a respectable lagoon)
7. Southern White Rhino (This list is obviously not in order, because if it was this would have been my number one pick, it is the last missing piece of the puzzle for a well rounded African Savannah, it is incredible that after one year we still do not have a single African Rhino in game)
8. Meerkat (It would be interesting to see how Frontier handles this animal, hopefully as an habitat animal, and find a compromise with a worthy enrichment station that activates their borrowing behavior. They are crowd pleasers in real life and hopefully that translates well into the game)
9. White Backed Vulture (for the same reason as the Marabu Stork, there is just something special about some broken fallen tree branches and these magnificent birds of prey resting on them, with some African ungulates in the background)
10. Clouded Leopard (This is a must for me. There was a mod of it, that was quite good, and I can only imagine what Frontier's wonderful team will do for this gorgeous cat, it needs to be able to climb a concrete tree though, they are extremely shy and secretive so keep that in mind)