I think we know the list, we keep asking for stuff and get either; it's on the list, it's planned for future updates, It's unlikely, it's being thought about, etc. With a bit of detective work, going through all the staff posts, I reckon you could come up with a list not a million miles off the actual one...where stuff is on the list? Well that is open to conjecture.
Yeah. Most exotic animals are legal in one state or another, as long as they're not wild caught usually. Piranhas are banned in the USA only in states where they could survive in a river system (when they get too big and people dump them). Here they would most likely die in the winter, so they're legal. Although why anyone would just dump them when people like me will happily pay for them, I have no idea.