B777-9 will (more than) challenge the A350-1000

UPDATE: Thank you for the comment! Of course I picked a wrong MTOW for the 777-300ER. I corrected it and the values coming out of it. The basic conclusion keeps the same, especially as the announced SFC reduction of the GE9X will be 10% rather than 7%.
Of course, even with the small increase in inner diameter of the B777-X a ten-abreast seating will be less comfortable than a 9 abreast-seating in the A350. And more capacity is always higher risk (for revenue vs. costs), but for all current B747-400 routes the B777-9 would be the ideal replacement. The A350-1000 will fly with lower costs per flight, so if you can fill the A350-1000 it will be a profit maker as well.
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The proposed B777-X models, the larger B777-9 holding about 405 passengers and the B777-8 with about 350 seats, should slash fuel burn per seat by 15% (B777-9 vs. B777-300ER) and about 10% (B777-8 vs. B777-200LR).
Is that possible? Let's have a look by taking a very simple approach and concentrate on the comparison

Dubai Air Show

If an article published by Reuters is correct, we will see a major order for more B777-300ER's from Emirates at the Dubai Air Show, which opens on Sunday. Rumors are, that Emirates will order another 30-50 of the long-range twin. They still have 41 B777-300ER on order. At the recent order pace that would be good for another 3.5 years. By then the first A350-900 aircraft should arrive. Ordering more B777-300ER could have the following rationalities then:

• Just more growth...well, it is Emirates!
• Dumping the A350-900/-1000 order altogether - unlikely!
• These will in fact be orders for a B777-8 or B777-9 - not too likely at this point, but not completely impossible!

Also, who knows - rumor is that Emirates will also order 30 more A380 - maybe they will announce to be the launch customer for the A380-900...