The best MOM aircraft already existed, it just needs to be redone. Just take the A300-600 and increase the range from 4000nm to 6000nm and all is good.
90t OEW, 170t MTOW, LD3 capable, composite wing, perfect freighter base. Back then Airbus had no chance as to increase OEW and MTOW to get range for the A330 but with new technology a 90t OEW A300-600 with a composite wing should have no problem to carry 30-35t out to 6000nm with 45-50t of fuel.
I think the A310 shaved another 10-12t from the A300 empty weight and added range. While the basic A310 configuration looks attractive, the way wings and wingboxes were build 40-50 years ago has changed dramatically. So it would mean an entire new wingbox, wing, suitable engine (...) and landing gear. The cockpit, avionics, cabin systems could be taken over from the latest A330NEO versions.
Even if Airbus would to willing to optimize an A330 version for an NMA like mission, OEW 75t, it would still weigh 50% more than the mass produced A321XLR. I think that a prohibitive benchmark for any new aircraft not offering a clearly differentiating efficiency. https://flyawaysimulation.com/downloads/files/3805/fsx-air-transat-airbus-a310-300/
The question for Boeing or Airbus would be if a smaller WB, 8 abreast and LD3 capable, could be designed lean enough, to also operate competitively on the many shorter flights, on top of competing with the larger, more capable WB's on longer flights. I think Airbus internally see the A310 as an experiment not to be repeated..
I wrote that in the post before yours, the design of the A300 is 40 years old but I do not think the fuselage is the problem. What it would need is taking the A339 and give it a new wing box and wing (together with a new gear), a new tail and take as much weight out of the fuselage as necessary.
The A310 failed mainly due to the fact that the timing was really bad and when air travel started to grow in the later half of the 80s and 90s the A330 was by far the better option. From 1993 the aircraft was almost dead in the production line
Nowadays I could see some market for an A300 sized aircraft with 6000nm range. Going forward it would need to sit in the middle of the size between a possible A322 and the A359, somewhere around 75-85% of the A339 cabin size.
It would complement the A321/322 when you need additional range or payload. Sub 3500nm the A322 would be the better option, but from 3500nm to 6000nm it would beat the A339 on economics and it could carry a lot of freight.
That is the space the MOM has to sit and that is why a 2-3-2 seems so out of touch, because it limits itself to fit into the market below 3500nm. I just can not see how anything else than a 3-3 aircraft can be efficient below 3500nm. But if you want to fly further you need to make the structure carry enough payload to make it worth while, so from 4500nm onwards the aircraft has to have some kind of lifting potential, more than just for passengers. Otherwise every route that has just a little cargo demand will be going to the 787, limiting sales in the upper end.
If we look at the A321neo today, there are nearly 3,000 frames on backlog and 500 delivered. Airbus does not need a A322 or a A330 light as it is. An A322 would just take orders from the A321neo and an A330 light would make live more difficult for the A330neo.
Boeing has to do something. Boeing is just hanging on in the 737-8 sized market, the A320neo has a backlog of 2,650 frames and 1,200 already delivered that makes 3,850 frames. The A320 alone matches the whole 737MAX lineup in numbers.
Boeing has no frame competing seriously with the A321. The only frame at Boeing matching expectations is the 787.
If Boeing wants to continue to be a player in the 130 to 250 passenger short to medium long haul market, they have to make their move. Airbus can wait and see what Boeing does.
If Boeing comes with a frame slightly larger than the A321, Airbus can bring a A322. Airbus has been working on designs regarding a new wing, including going all electric on that wing. The all electric part, leading to significant weight reduction, has flown on the A320 testbed. In regards to the wing itself, Airbus has now done several carbon fiber wings.
If Boeing comes with a frame significant larger than the A321, Airbus could go for a A330 light, a redo of the A310. Same fuselage as the A330, lighter wingbox lighter MLG, same cockpit as the A330. It would be a stubby frame significantly lighter than the A330. The new things needed would be a new wing and right sized engines.
It is sometimes forgotten how related the A300/310 and the A330 are. Many advances in regards to the modern 2 engined wide body had been tested on the A310 and influenced the design of the A330. Airbus has never been bothered about not keeping the type certificate for the new model. They changed what needed to be changed.
In regards to a 767neo from Boeing, I hardly believe that that would be a good move. Yes the newer 767 gave the older A300/310 a hard competition, especially because of more range, but than Airbus brought the A330 and sales of the 767-300 went down and the 767-400 did never really take off. The 767-400 was supposed to hold it's own against the A330, but did not.
Boeing brought the 787 to win the market back from Airbus and it took off. But during the years the A330 did hold it's own.
Why would a 767-300neo or 767-400neo do better against a A330neo, than the 767-300 and 767-400 against a A330ceo.
And that brings me to the widebody 7W idea. Either it is not economical against a 8W design, being relatively to heavy. Or one builds a frame for passengers with little cargo capacity and that means a severely limited market.
There is a reason the 8W A330 won out against the 7W 767 and why Boeing went to 9W in the 787. The answer is economics.