User blog comment:Sim533/Medieval World Preview out/@comment-2233791-20140528063850/@comment-2233791-20140529065144

Found a quote from the leading developer to answer your question.

Q. How many worlds are you hoping to have at release? How easy will it be to add in new worlds once the game is live?

LP: We will have several worlds in the game at launch. The ones we have revealed are Pirate, Medieval, and Space World. We’ll be revealing information about the additional worlds in the coming months.

Adding worlds is a pretty straight forward process for us, and we will continue to add new worlds at a regular pace post launch. The launch themes are based on very classic play themes, but post launch we will start to add locations that are a bit more wacky and unusual.