The killer feature of whatever game engine replaces Unity in developers' hearts and minds is going to be the platform delivery aspect. Once you can press a but

The killer feature of whatever game engine replaces Unity in developers' hearts and minds is going to be the platform delivery aspect. Once you can press a button and get Win/Mac/Linux/Android/iOS/etc versions of your game built, you're in business. All the higher-level features (3D, ray casting, etc) will be contributed by the community over time.