I second the questions made by the OP. The lack of shader extensibility is making my life very hard with UE4 (current project migrated from Unity, where shaders are fully and directly accessible). Honestly, I think it’s unbelievable that at this point UE4 does not allow for direct addition of custom shaders (fragment shaders included). There has been words from the staff in the forums in the past acknowledging those limitations, but never got clear whether something has been done in the direction of improving that.
If you think how greatly important shaders are for graphically authoring a game (not to mention to implement advanced techniques and also procedural generation), it’s of great concern that this subject does not even appear in the roadmap at all. I have tried before in other forum threads, but considering that this one is right on the point, I will try once more: could any Epic staff give us some words of comfort on this subject? Please, Epic, consider freeing us from the shader-cage imposed by UE4