A return to fixed 50mm (or 35mm) lenses as kit lenses?

Actually, many zoom lenses in the 70's and 80's were almost as good as, or as good as their prime counterparts, and initially more expensive due to their more complex construction.

Over the years the addition of autofocus, stabilisation, and high speed motors has added further complexity to the design, and therefore made sacrifices. You will not find a single kit zoom lens that is good wide open at a variety of focal lengths. Perhaps you may have a sweet spot at one focal length, and a ballpark aperture of f/8-11.

The reason prime lenses are not included anymore is because the general camera consumer these days is an idiot and expects their camera to be able to do anything. The average armchair photographer wants to be able to take every conceivable type of photo from sitting in one location.

Hand them a prime lens and watch them struggle with it. The concept is beyond most people, and as most DSLR buyers will never even know the exposure triangle, aperture has no relevance to them.

Yet they all want the best quality body, without even thinking about the lens.