May be a high aspect ratio wing (may be struted and foldable) could give B737 design another last shot of life
Very doubtful. I expect the 737Max to get an engine PIP with cmc turbines to improve fuel efficiency. A small PIP is coming in 2021 for a 2% gain. In 10 years time I expect an improvement in SFC to reach 5%.
The 797 effectively covers the 737 weakspot and allows the current design to keeo selling for longer. The 737 is very competitive on short haul below 200 seats and 3000nm. In fact in many areas it is superior to A320 family as it is sized perfectly for just under 200 seats with 4 flight attendants.
The A321 is in a much better position long term. A carbon wing with more fuel capacity and newer engines would bring it very close to a clean sheet design. The cockpit, landing gear height and maximum takeoff weight are similar to what a cleansheet design would have.
The 767 was a much lighter shorter range model than what it became. It started as 3900nm range 767-200 followed by the 767-300 at the same range. Then grew into the ER models.
The original 767-200 wasnt much lighter at all. Only 2T or 3% lighter empty than the 767-200ER.
My point was the original 767-200 still had the large wing, centre bulkhead and heavy landing gear to allow the maximum takeoff weight to go from 142T to 186T or a massive 30% increase.
If this headroom wasn't built into the 767-200 it would have been built with a much smaller wing and would have had an empty weight maybe 10% lighter.
So the 797 might have a maximum takeweight similar to the 767-200 but it's wing and landing gear would be sized correctly (smaller, same span, less area, higher aspect ratio)