Here's the answer from the pinned FAQ post:

"Will new content be added to my world I currently are playing on?

New content such as tar pits, mountain caves and Mistlands in the future will not appear in areas that have been already generated. Areas are generated 300-500 meters from a player's location. "Exploremap" and "resetmap" has no effect."

"What will happen to my world when the game is updated?

We can't know this 100%. The things you have already built should still remain, and ideally you will be able to keep playing on your existing world. However, it's not certain that you will be able to access all of the new game content without starting a new world."

https://steamcommunity.com/app/892970/discussions/0/3383905288030494726/