I can see the quest for a solution to this becoming more urgent as the years go on. In Asia, the younger generation is noticeably taller and wider than their parents and this has happened inside a generation. For today's teenagers growing up in Japan, Korea and some of the other Asian countries, there is often no difference in size between them and Europeans. In the USA, they seem to have exhausted vertical growth, in favour of girth.
That said, flying is becoming a demand-derived business, like shipping; the demand is there and will be satisfied one way or another.
Personally, I like the Southwest example, cited by our moderator. Wonderfully phrased in politically-correct language, far beyond my jaded ability.
But otherwise, I wonder if it is possible to design a seat which can be varied in width (and maybe even legroom for our friend FanPilot). If adjustment past a certain point were required, a charge could be made.