Emirates is going for A350-1000 instead of A350-900

Emirates is considering swapping its order for 50 Airbus A350-900s to A350-1000s as Airbus works on finalising design of the stretched variant.
In November 2007, the carrier ordered 70 A350 XWBs, initially specifying 50 of the baseline -900s and 20 -1000s. But Emirates president Tim Clark says over the last three years the carrier's network has matured to the point where it "can no longer tolerate anything under 300" seats.
Emirates is slated to take 290-seat A350-900s from April 2015. The A350-1000s would be a better fit, but the longer wait must also be considered.
"It [the -900] is now appearing too small," says Clark. "So we may slip the order to the -1000, but the -1000 hasn't been frozen yet. We haven't decided quite yet which one we'll take. We're actually playing around with how this order fits."

The A350-900 is scheduled to enter service in 2013, while Airbus has provided a 2015 entry into service date for -1000 stretch. Clark says the only option if Emirates wants to take A350s in 2015 is to stick with the -900.
Delivery dates for the A350-1000 are not likely to be firmed up until the design is frozen, which could take time as airlines continue to press Airbus for changes. Clark says with the current design the -1000 will not have a range or payload comparable to the Boeing 777-300ER.
"Airbus compares the -1000 to the 777-300ER. I've told them in no uncertain terms it does not. I see it as a 320-, 330-seater which will be very economical on missions up to 10 or 12 hours," he says. "The notion that it would fly from Singapore to European gateways in the winter months with 100 knots on the nose is a bit of an ask. We've suggested they need to come to grips with that, which means they need to increase the takeoff weight and they need to increase propulsion."
The aircraft is slated to be powered by Rolls-Royce Trent XWB engines but Clark is "not sure they will do the job".
If its -900s are delayed beyond 2015 or it elects to wait for the -1000, Emirates can avail of the "safety net" of 30 additional 777-300ERs ordered last year. The airline's original thinking was for the A350-900s to replace its 777-200s, A330-200s and A340-300s, but it has the flexibility to retain these aircraft for longer.
In 2007 the airline ordered 70 A350 XWBs: 50 -900s and 20 -1000s

src: flightglobal.com