Even in the 'old days' I've never heard Arctic/Antarctic used interchangeably; they refer to two completely different parts of the world. As I said, 'Polar' refers to both, which is probably what they might have used back then if they were making a 'Frozen Planet' expansion pack or something. I don't think it's about people being specific or lazy with language, it's about being correct and incorrect (especially for Frontier, which has marketed itself as a leading force in terms of accuracy for its games).
As to the rest, the gaming industry moves too fast now for the same kind of 'expansion packs' we used to get. People don't have the attention span anymore to wait that long for new content. Hence, DLC, small bursts of new content on a more frequent basis to ensure your game has a consistent following. Even with Planet Zoo we saw this happen, with a huge lapse in general interest between the Arctic Pack and the South America Pack. People are just generally spoiled for choice in the modern age, so it's a lot easier to move on to something else when you get bored with what you are doing (and, as much as I love Planet Zoo, the replayability of it isn't huge, since everything in the game requires a lot of patience and time).
In saying that, there's always the chance we might see something more substantial come along. A lot of people talk about Frontier adding in birds to the game, for example, but a four-animal DLC pack wouldn't be sufficient to cover such a theme. I'm not at all confident we'll ever see too much in the way of aquatic animals (there's no system in place for diving/underwater swimming, and Frontier has said that it would be more difficult to implement than the climbing system was), but if we do then there's a chance we could see a host of aquarium fish show up alongside a few key habitat species (sea lions, seals, penguins).
As to the crux of your wishlist - I would say that the meerkat is probably the most highly-requested 'non-aquatic' animal on that list. It's certainly a common sight in just about every zoo in the world (even the smaller less notable ones). Many people have suggested that it might be too small to successfully add to the game, but I really don't think that's an issue; Frontier did, after all, add the miniscule compsognathus to Jurassic World Evolution which is a game on a much, much bigger scale than Planet Zoo.