http://leehamnews.com/2015/07/14/air...-900lr-likely/

SQ might push Airbus for a A350-900LR. Unlike the 77L, which is basically a 77W with the 772 fuselage, the A359LR would be an "improved" version of the A359, increasing MTOW by 12 tonnes and adding 18,000 L of fuel. Boeing is still producing the 77L and is looking for buyers. A few weeks ago, EK was said to be in discussions with Boeing for an additional 15-20 77Ls. Next year, the 77W is scheduled to be given the option of a Performance Improvement Package, reducing fuel burn by an additional two per cent. This PIP also applies to the 77L. The 77L has much better performance and fuel burn compared to the A345. However, the 77L would have to be delivered with the aft fuel tanks to make EWR-SIN. I expect Boeing to push hard for SQ to, at the minimum, lease this latest version of the 77L before the 778X can be delivered next decade. The 777-8X already has sold better than the 77L. SQ might be able to secure rather favourable terms since Boeing needs to finish out the 77L/77W line. While the A359 will undoubtedly be improved overtime, I doubt Airbus will try to convert this into a A359LR, considering the ME3 is already locked in with the 778X for ULH flying. If SQ had their way, they would have Airbus begin the A359LR programme but Boeing might offer them a short term solution that they can't refuse.