I don't see the A350 (which sounds like a reworked 332, an aircraft SQ has rejected before) as a runner. I think the real reason for SQ's decision is that it wants to see the effect of the new low cost carriers on its short haul operations. Remember that the old A310s flew (with a few exceptions such as flights to PER and Japan) within a 4 hr radius of SIN; this is the same range as the low cost carriers' A320s and with the competition they're likely to provide, the 7E7-3 might not necessarily be the best idea. Or at least, they'll want to wait and see how much of an impact the new carriers will have on their existing operations.