Building on what MaxQ stated, your comparing the economics of a stretched aircraft to that of a shrink. The 747-Adv will make the 747 as a whole lighter and more fuel efficent, while an increase in seats brings seat/mile cost even lower. Conversly, shrinking the A388 would make an aircraft heavier and less efficent per seat/mile. I would be *very* suprised if the A387 would have economics that would make it a serious contender without
the 747-Adv in the market.
The A387 would have commonality with the A388 which is a bonus for airlines already ordering it. Problem is, the 747-Adv is tailored for the airlines who want a slightly bigger aircraft than the 744 but don't want the risk or quite the capacity of the A388. These are airlines like CX
If Airbus has a design that would win *new* customers to the A380 family (be it A387 or A388) they would be acting on it by now. Enough A388 design work is completed for Airbus to study a derivitive, and since they are not proactively courting airlines, I don't think the A387 concept has much potential. I think the A387 went out the door when SQ
demanded their noise requirements be met a