Most weight should be in the Al wings? Sort of like the 777-X program, the older wing hold a lot of weight that can be saved be changing to cfrp. But that would add cost to the cheap neo program, cost and complexity.
But for sure, the A321 could do with a larger wing.
The A321 would be a perfect frame to do a 757 sort of program on, but that is too late, the next generation NB
will not have the same cross section probably.
I think there is a much bigger market for long and thin, its just that no efficient modern option exists, a dedicated frame for this purpose. In 15 years most of today's 767s and A332s and 757s will be put to pasture, the best option would be the 788 but it is still a lot of frame to fly thin routes up to 4500nm.
The 757 was never intended for its current role and a dedicated frame for this role with a tad more capacity and a lot better economics could be a potential big seller. Take some of the upper market of the NBs to save them weight and take some of the lower market of the smallest WBs to make them better for longer routes.. OEW about 55-60t, 220 seats maximum and 4500nm in bad head winds.
Will fuel cost force airlines to fly more optimal sized frames in the future? Most view the 788 as a 8000nm frame not a 4500nm frame...that 8000nm adds a lot of weight on that thin 4500nm route. This would be a new size class with nothing in the current market that compares.