I think the end of 2020 will tell the tale of this games future. I think it's always been guaranteed there will be a fourth paid dlc by the end of December, as it will have been nearly all of August and all of September, October and November since the Australia pack released. As far as the contents of that goes, there's no reason to expect anything other than four habitat animals, an exhibit "animal" and a couple hundred scenery pieces.
For me, the size and quality of the free update that comes with it will be very telling. If they've been working on something significant this whole time, something game changing and that the community has been asking for, then I would say PZ still has a bright future. If the update is small, lackluster, contains small or meaningless changes, a host of new bugs in addition to not fixing old ones etc. that's when I will fully give up on both this game and Frontier. So for now, as depressing as it is, we just have to wait and kill another couple of month's time to see what will happen.