"They won't accept anybody's ideas no matter what" is untrue. Like others expressed before, they do consider the META-wishlist, which has been very evident from the last 3 DLCs. They also listen to specific wishes of the community regarding new behaviours, which is why we now have digging and burrowing in the game. I think they deserve a lot of credit for the new animals we got this year, as well as changes in behaviour and new construction pieces.
However, in a game with perhaps hundreds of thousands of players (basing this on the fact that the subreddit already has over 70.000 members), it would be impossible to listen to literally anybody who comes to them demanding a specific animal. I honestly think you've been a bit rude by approaching a developer personally and simply asking for this species (which will inevitably come into the game at some point), and his response is very reasonable.
I agree with the post above and if I were you I wouldn't worry too much about getting a leopard. It's high on the list and we have at least one more year of DLCs, so it will make it in at one point. But if they give all popular animals now, the game would be dead in a few months and I don't think anyone of us would like that. They also need money to develop the game and perhaps finance a sequel. Meanwhile, if popular animals remain demanded, the game could live on for up to five more years.
Back to the topic for now, since I came to this thread because I'm also interested in more invertebrates. It seems like we're getting a Lord Howe's Island Stick Insect soon (based on leaks), which is a cool and original choice. Next to that, I would love to see:
- Orchid Mantis
- Toebiter
- Coconut Crab
- Cave Cricket
- Hercules Beetle
- Atlas Beetle
- Tailless Whip Scorpion
- Hermit Crab
- Giant African Millipede
Horseshoe Crabs and Japanese Spider Crabs would also be amazing, though I don't know how they could be implemented. The current exhibit system wouldn't work, and habitats also doesn't seem like a perfect idea.