Neither a smallish 787 or an updated 767 will solve Boeing's single aisle problem. How can widebodies help replacing the overstretched and shortlegged ExMax
2 aisles require more cabin crew and a low fares airline will only fly with what the rules minimum requires and that is 1 per 50 passengers.
How do you do sample safety demos with 5 cabin crews in a 250 seat plane with 2 aisles and no back of seat screens.
How do you, to avoid delays waiting for passengers, offload that 1 bag quickly if the luggage is in belly containers. Not to talk about all the containers and container handling equipment needed.
And no freight advantage because the likes of Ryanair don't do freight, normally.
Do they come with onboard steps, to avoid waiting for availability of external steps, for prompt offloading.
Do they fit in the relatively narrow and cheaper stands of most airports.
Besides airport parking fees are per tonne.
Widebodies might be more prectigious to fly, for some, but they don't suit 1-3 hour short hops which is sample Ryanair's bread and butter.
And they are the likes who have pressed for the more passengers = longer 737 with more economical = bigger diameter engines.