I have been thinking about what fuselage width A&B will go for with the 733/320 replacement craft.
B have stated just about every possibility and now saying could have 3 different fuselage widths. I think this is unlikely.
My first guess is that the next generation "narrow body" will be about 20" wider than the current 737.
This would allow the option of either single or twin ailse.In twin aise mode seats would be roughly the same as to-day but with 2 ailes and 2x2x2.
In single ailse mode the carrier could either have wider seats or a wider ailse. I think most would go for a slightly wider seat and a much wider ailse to make boarding and deboarding easier.
Second guess is that the fuselage width will stay approx same as at present, to keep weight down.