I am cautiously optimistic about the animals identified via datamining as being part of the initial roster. It may be that they are developing some of those items to support the animals inclusion down the line, these animals may not be ready for prime time at launch.
I think part of the reason they've been tight-lipped about the full roster is that some of them are still likely in development. By saying there will be "at least 50" animals, they are setting expectations. I can see us getting
way more than 50 animals or something like 55 or so (plus the deluxe version animals). Kinda all depends on what goes on behind the scenes, IMHO.
I think it's fair to say they will be available eventually, though! Most of these are pretty common/popular zoo animals, and it would be strange for them to include signage, statues, etc. for any animal without having it in the game. But I'm not convinced that they will all be available as part of the initial game. I'd love to be wrong, though!