Just so people are aware - the big JSONization push has had customization as it’s primary goal. While the WorldBuilder will certainly have some options available itself, I want to stress that it’s primary purpose is to lett you choose which JSON files you want to use, and have multiple worlds that use different combinations of them.
Bot most of what has been described so far can already be modified through the configuration files, and we hope to get to the stuff that hasn’t.
Building a world to your exact specifications might not actually be easy, because there are so many things that entails, but at least it means that once you’ve got one you like sharing sharing it will be trivial, and you can play worlds others have configured as easily as downloading a folder to the right location.