Just an observation:

The reason for past 4-engined aircraft was that engines of the time were too unreliable. The plane could continue to fly with 1, 2, and if not heavily loaded, even 3 engine failures.

For the past 20 years, with the advancement of engine reliability, there was a movement towards ETOPS, however even the 777 is not allowed to overfly some areas of the globe (south pacific routes, polar routes) even with 207 minute ETOPS. Those routes seem to be reserved for the 4 engined aircraft.

With reliability the way it is, and considering the extra cost of having to maintain each additional engine and attached systems, why not renew the trijet concept? It would achieve ETOPS-free operation, at a lower cost than a 4-engined aircraft.

Maybe the MD-11 was not so bad an idea, except that it was 1) still too much of an old DC-10, 2) pretty costly for the time, 3) Had a few handling problems plus was saddled with a sad history of accidents (even though not all it's fault).

I can just imagine a 3-engined version of the A3XX with three 100,000 lbs thust engines.

Charles