In recent years we have seen the A321CEO leading to the A321NEO, leading to the A321LR and now Airbus is studying an A321XLR. The MTOW would raise to over 100t, adjustments would be made to the wings, engines, landing gear and a new integral fuel system/ storage. Capacity would grew a bit versus the old A321; LCC's are squeezing in every seat they can. Door relocation, smaller lavatories, ultra slim seats etc. But not substantial, it's the same A321 fuse. https://www.flightglobal.com/news/articles/airbus-getting-serious-on-a321xlr-next-year-453906/
Airbus has been looking at an A322 stretch since the late nineties.
.. . . .https://www.flightglobal.com/news/articles/airbus-supplement-a320-family-28463/A further stretch of the A321, unofficially dubbed the A322, to rival Boeing's extended 757-300 has been studied, but seems unlikely to go ahead. "I don't think there will be a stretch of the A321: it would simply trade range for payload," says Brown.
Things have changed. 20 years ago, an A321 with 4700NM range or 240 seats was not on the radar Market demand, MTOW growth and new engine technology changed the picture over the years. With A300/310, Boeing 57 and 767 fleets getting real old, airlines are knocking the doors for efficient medium range capacity.
A meter of A320 family fuslage weighs around 600-800kg. The A321LR has an empty weight of around 97t. If the MTOW is increased by e.g. 4t it becomes around 101t. If that MTOW is maintained for an A322 version of say 4 meters, 2.8t is consumed by additional empty weight. An additional 4 rows/ 24 passenger /luggage would come in at 2.4t.
The A321LR has an advertised range of 4000NM with 164 passengers, as Bjorn Ferm sketched: https://imagr.eu/up/0GAt7_PR-diagram-1024x588.png. A MTOW bump of 4t for an A321XLR/A322NEO probably translates in a payload bump of 1.2t for an A322. You have to use the added capacity. Theoretically you could go above 260 seats high density, but if we assume a 200 passenger 2 class payload, that results in a useful range of 3000-3500NM. JFK-LAX is 2200NM, 3000NM is probably covering 90% of all commercial flights. With 250 seats single class, 2500NM should be doable for an A322.
Tail strike, clearance
If the fuselage is lengthened for a A322 by 4m, that would mean the tail section be lengthened by approximately 1.5m. That will result is a reduced maximum lift-off angle, which mean a slightly higher V1, longer runway etc. a thrust bump of 3-4k lbs on the engines could solve this and seem foreseen in the PW1100 and LEAP-A. Apart from that, the A321 has never been a runway hog, it seems for most operations a marginal longer runway requirement would not be a serious restriction, if they can handle 739/10s too.
The A322 Business case.
The market seems to be asking for 250 seats medium range, if Boeing and Airbus are to be believed. If an A322 is included in the ongoing A321XLR study, using the same MTOW, engines, LDG, wings, fuel system, additional investment and risks would not seem prohibitive. The markets in the US, Asia and Europe seems extensive for cheap, up to 250 seat aircraft. CASM would probably be real competitive compared to bigger twin aisle aircraft.