I totally understand and agree, that's why I wouldn't worry about open source or even building it in Unity. What I meant was keep developing as you do, maybe just look into / get someone to create some sort of hook between Kenney -> Unity (or even Kenney <-> Unity, though the file format might be an issue I guess). Or like I said, could you just put it in the Asset Store as a standalone app to boost sales? I'm pretty sure I've seen some standalone apps there without ANY Unity integration..