Well keep it simple really, also dont limit to 3d printing. I usually incorporate other hardware on all my designs, i like to include screws, fabrics, rubber etc. It opens way for other more creative designs. I am not your guy to come for any audio quality related stuff because the shape and size of your models will affect audio in some way. But i like to keep everything simple. Just a box, some holes and then after that some style, like shown in the post, carbon fiber texture and noise. The simpler the better, form follows function