While I'm not a user of this editor, this seems like great news. 4coder receives significant attention via the Casey Muratori's video streams like Handmade Hero, and opening it up is sure to produce some positive growth for the development/community side of the project. The combination of popular development livestreams and FOSS tooling utilized in those livestreams seems like it could be an important part of making…
This is not a "opening up" of anything but the source code, with a permissive license. You're free to fork and change anything you want, but it won't be upstreamed ever as the author did the open sourcing because they are stopping maintenance of the project.
So this is more of a "closing down" with the gift of leaving us with the source code. And for that Allen Webster, I thank you!