While they seem to be on the way out, a neo option would be a quick solution to the mom problem and it would go hand in hand with the 757neo given these aircraft were developed in parallel
The wing is pre-CFD. There is no FBW system. There isn't enough clearance under the wing to install an engine with an optimal fan diameter. The fuselage has two aisles for 7 passengers. Aisles do not earn revenue, so the cross-section is the least efficient possible for a twin-aisle aircraft.
Best to start from scratch and come up with a new model that has upgrade potential.
The 767 ustilizes FBW for the flapperons and spoliers so to say there is no FBW is false. The 737 has the same situation now with FBW and engines, yet it works. The 767's wing isn't much older than the A320's yet the A320 is still considered great, it can't be that Airbus did that much of a better job only about 5 years later. 7 across being terribly inefficient is way overblown, if it was so bad the 767 wouldn't have killed off the A310.
Now with that said, a 767 max is something I don't see happening. If they were to do it however I believe they could fit newer engines as the 787 seems to do so with the same amount of ground clearance. They could also put the 777X's cockpit in it. They could even convert it fully to FBW and even give it a new wing if they thought that would work, but I think after what happened with the 747-8, they don't want to do a project like this again in case they reach the same outcome. I do think the 767 has more upgrade potential than the 737, it just won't get a chance to ever prove it.
The 767 has no FBW and the 737 has no FBW. FBW is the name for controlling the 3 axis of an airplane with a flight computer and the inputs of the pilot are not direct to the control surfaces but into the computer.
Calling computer controlled flapperons and spoilers a FBW is just simple grandstanding. Like calling a car with an electronical controlled injection and ignition, a computer controlled car.
The 767 was an old design when it was new, whereas the A320 was a revolution, first commercial aeroplane with a digital FBW, it is well possible that one company does design something new whereas the other company keeps to old solutions. The 5 years time difference is irrelevant. The wing of the A320 family, if rather small for the A321, is still a very efficient wing today.
In what way did the 767 kill off the A310? There were 249 767-200/200ER sold and 255 A310, pretty even I would suggest. The A300/310, than a revolutionary design starting off the twin engined wide body, was time wise a far older design than the 767, It was replaced by the A330, that than did away with the passenger 767.
There will not be a 767 max. The 767 was killed off by the A330 on similar engine technology. Boeing developed the 787 as the replacement for the 767 and an answer to the A330.