I saw this project a couple days ago. From what I understand, they basically constructed the engine for a homebrew game, and they are providing a set of tools needed to create content for it (aka hack it). From a romhacker's perspective, it is similar in ease/difficulty to making content for any NES game that already has had a set of good tools created for it. The main advantage is that they freely allow you to use, edit, and possibly distribute that content. I actually didn't see any mention of distribution, so I'm not sure about that last bit. They only mentioned playing the game that you created yourself, not allowing others to play it too. The quality of the tools and legal right to distribute your created content will determine how big of an impact this will end up having on the homebrew scene. There is also a bit of a risk that the homebrew scene will get flooded with low effort productions. I'm sure there will also be some good ones too though.