The only reason there is this notion that we are nearing support is based of off Planet Coaster's life span. The game was released in late 2016 and received its last DLC sometime in April 2019 I believe, and in November 2019 Planet Zoo released.
So far there is no indicator that we're nearing the end and every single time there is DLC around the corner, the "end is near" conversations arise again. I think the difference here is that Planet Zoo offers online play with Franchise mode. I suspect that sometime down the line franchise servers will be shut down, and that for me will be one of the most telling signs that the game is done. Until that happens, I have no reason to believe we are done, and I am looking forward to all the future DLCs and updates, whatever the amount may be.