Having not playing Planet Coaster 1 or 2, but having seen the fairly universal dislike towards its approach from players, I'm a little wary of a Planet Zoo sequel, but we all know it's coming sooner or later. It of course has the easy upside of aviaries and aquariums, scalable construction pieces (PLEASE!), changes to exhibits (1x1 exhibits for insects as a start) and a pathing rework, I also heard that PC2 allows multi-threading which would be pretty massive for Planet Zoo, considering large zoos literally have to not include animals in order to run at a playable FPS. There are also so many small things like adding drinking fountains, playgrounds, binoculars, camera improvements that would go a long way. I think if it's done well a sequel would be incredible and make the game significantly better.The more I play Planet Coaster 2, the more I WANT things to stay mostly the same between PZ and PZ2. The new controls, the new grid highlights, the new UI sorting of building items, the oversaturated graphic, the low foliage quality, the missing multi-recolor tool, the constant clicking and more all are so TERRIBLE and tear the fun out of me so much while playing, that ME, who was always looking forward to a sequel and justified its possible existence and was really looking forward to it is HONESTLY considering never to play a sequel until I am guaranteed they do NOT change controls and UI.
I'm still trying my best to learn PC2s way, but I feel more and more it has been programmed by people who never played a Planet game in their life.
And unpopular opinion, but I hate the new path system, but that is at least something I can probably learn to use down the line. The rest, espacially the new multi-select tool and the weird item sorting is something I will never get used to though, and it was the worst decision they ever made.
But I do fear a lot of the things they could do such as what you've said, and omitting species seems very likely unfortunately. I'd be cautiously optimistic and if I'm being honest I love this game too much to not buy the sequel when it's released, but my response when playing the sequel could vary massively
With that said, honestly the timeline between DLC 19 and 20 makes it seem plausible that planet zoo 2 is a lot further away than we probably expected only a month ago. Whether that's in response to PC2 and they want to shore up a bit of easier money through DLC or it's always been the plan to do it this way, I don't know. It's all speculation at the end of the day, but it seems highly unlikely they have such a short turnaround on DLC then stop making them straight afterwards