Can We Still Invent A New And Sound Opening?


I'd imagine, everything worth looking at in the first ~5 moves has already been studied thoroughly and either discarded as sub-optimal, or accepted in the theory. You can certainly make up openings that aren't very popular and playable, but you will always be outplayed in the opening by an opponent sticking to the theory.
If you want to avoid playing by the book at start, take a look at chess 960, there you will have to think outside the box from the very first move.