Boeing has confirmed that a stretch of the 777-9 is technically possible if customers express interest.
"We have the ability to do it," Boeing Commercial Airplanes chief executive Ray Conner told reporters today. "If somebody wanted more capacity, that's a pretty straightforward deal for us to do."
Boeing is developing the 777-8 with about 350 seats and the 777-9 with more than 400 seats. A further stretch of the 777X family would give Boeing a twinjet with range and capacity closer to the four-engined Airbus A380.
But Boeing's ultimate decision will be based on customer interest, Conner says.
"This could be an extension of the family depending on what the customers really want. It would be more about what the customers are really looking for," he says.
If pursued, a so-called 777-10 would become the sixth passenger-carrying airliner planned to be in the market after 2020 with more than 350 seats in standard configuration, joining the 777-9, 777-8, 747-8 Intercontinental and Airbus A350-1000 and A380.
Airbus executives have expressed concerns about launching an "A350-2000" with capacity for 400 seats, saying the market segment could become over-saturated, with new variants simply cannibalising orders that would have been placed for existing types.
But Boeing does not appear to have lost enthusiasm for the potential of the largest segment of the market to absorb more products.
When asked about the risk of the 777-9 cannibalising orders for the 777-8, Boeing's chief salesman John Wojick expressed only confidence.
"I don't see us cannibalising ourselves," he says. "We've outsold them four-to-one since the launch of the A350-1000 [in 2007] and it continues to dominate the marketplace."