I was originally a Kickstarter backer when the developer was advertising the game as intended to be open-sourced, but then open-source became a Kickstarter goal so I withdrew the backing.
Looking at the Kickstarter right now:
"Stretch Goal 3: Modding Support
This goal includes three things in specific:
The game source code will be publicly available! ... The code will be released under a license that prohibits using it for any commercial activities, and requires you to share-alike any modifications you make. The release will also not include any assets, so you'll still need a copy of the official game to play it."
The license for the code is zlib now, but the assets remain closed. I think that is a fair trade.