I would love it if they added an option that makes you unlock species as your zoo rating increases, it is one of the important progression aspects that PZ lacks as a zoo game and would feel pretty fresh.
Also thinking about a possible islands pack it wouldn't be that different to what conservation or twilight were, besides, nobody really cares about how consistent the theme is as long as the pieces are useful and the animals added are wanted. A Sumatran tiger, for example, would be a horrible idea, it hardly even represents an insular endemism to begin with lol and no, the community wouldn't welcome another tiger because surprise! we already have 2 tigers in the game, honestly why am I even explaining why adding a 3rd tiger is not a good idea? It obviously isn't xD
Also thinking about a possible islands pack it wouldn't be that different to what conservation or twilight were, besides, nobody really cares about how consistent the theme is as long as the pieces are useful and the animals added are wanted. A Sumatran tiger, for example, would be a horrible idea, it hardly even represents an insular endemism to begin with lol and no, the community wouldn't welcome another tiger because surprise! we already have 2 tigers in the game, honestly why am I even explaining why adding a 3rd tiger is not a good idea? It obviously isn't xD