Maybe going to full airliner size in the first step is just too big of a delta to take on at once. A flying wing business jet might be an interesting intermediate step (especially interesting for extravagant billionaires who would like to impress in style, I guess).
That's a nifty idea: put all the fuel and luggage out towards the wings and the passengers down the center. No more discomfort for passengers (during turns and turbulence) and you'd still reap the benefits of the BWB design. Though this would block window views...
MIT also came up with D8 or double bubble (see: https://www.nasa.gov/content/the-double-bubble-d8-0) but that, too, was 9 years ago
It certainly seems as though we're stuck in a local minima w.r.t. commercial aircraft.