I won't open-source the engine, at least for now ¯\_(ツ)_/¯ But still I would like to get some help.
If you are willing to contribute to IDE, please contact me on Discord or at Telegram (@CoMiGo). I have a repo, automatic build pipeline, linters and stuff, so everything is ready for collaborative development.
Ok I had a better look at the engine. Forgive me if my assumption is incorrect, but you are already releasing it with the entire source code. It's just some JS bundled with nw.js and some node modules + minified external libraries (pixi and dragonbones).
Edit: Ok, I might be wrong here- bundle.js seems to be minified and containing some ct.js code
In any case, if you do decide to open source it, please dont use the GPL license, as its viral. Most successful os game engines go with the MIT license