Roller Coaster Tycoon World missed it's original December release window with little fanfare, however according to publisher Atari, the game will come to Steam Early Access on March 30, 2016.

This comes as an interesting move for the game, especially because it had never been mentioned within the community before. To that extent, here is Atari's explanation on the game's Steam page:

As some of you may have guessed, we’ve been silently running a large test group with some members of the community since the beginning of the year. We’ve made so much progress with this group - getting invaluable feedback, testing ideas, and more – that we realized how much of a boon letting the rest of the community in would be in shaping our game. We cannot thank this group enough for their passion for the franchise and their contribution to the game, and for inspiring us to let the rest of you into the world of RCTW.

We also want to thank our developer, Nvizzio, and the QA team, who have been working tirelessly on this project. The Early Access version of RCTW includes a ton of content and we hope you will greatly appreciate the progress that we have made since our last public Beta.

This is the beginning of a new journey. RCTW was always going to develop and improve as time went on. Now you will have a direct impact on that process. It is only with your feedback, your input, your passion, and your creativity that we will bring the game to new heights.

To follow this statement, Atari made it clear they have no designated time they expect Roller Coaster Tycoon World to be out of Early Access. They intend to sell the full version as soon as all of the prospective features are added to the game.