This is kinda similar to what Caves of Cud did. Pretty much wrote the entire game from scratch and then used Unity as a dumb renderer/UI handler/multi platform

This is kinda similar to what Caves of Cud did. Pretty much wrote the entire game from scratch and then used Unity as a dumb renderer/UI handler/multi platform support. When the licensing fiasco happened the creator spent a live stream "converting" it to godot. He didn't open godot until the very end - just to start a thread with his code. Nor did he open unity at all either. Reminded me of your idea.