According to Wikipedia, the full completed version game of Planet Coaster is due out "Q4 2016". Maybe a month or two or three at most.
What I would like is water, all the rides in the Planet Coaster official announcement trailer, and the delete/bulldozer tool so we can use it to delete anything and everything we want. The bulldozer does work for coasters and rides, currently with the Alpha 2, but not for everything. Maybe there may be an Alpha 4 then they'll go straight to Beta then final version. But it's down to what sort of schedule Frontier has for the game.
But for an incomplete game, Planet Coaster is fun and really good. It's playable without lots of issues. And I love the ideas they put behind the game. It looks great. Easy to use building tools. And you can play and create your own fun world. It's like Minecraft. Just without multiplayer and mobs. It would be interesting though if (unlikely) they made this game multiplayer. You could play with others with your Frontier account, you can join their created worlds and play on them, and they could join your worlds and play on them. The Sims 4 is also a good simulation game too. But it also has no multiplayer. I don't really mind if they keep this game single player.