This is going to be a very hotly fought order and indeed, although EK is the focus of this thread, I can see many other carriers - CX, BA, IB etc - deciding between the A350-1000 and 787-10. I would expect to see the latter formally launched within the first quarter of '07.
If I were a betting man, I would say that EK's already stated interest in the 747-8I will have an impact on the decision; it wouldn't surprise me if EK decided to become a launch customer for the 787-10 and order 747-8Is (of whatever length, as Boeing hasn't ruled out building the smaller model of the 747-8 specifically for EK's requirement - and that decision could itself be crucial).
LH is also in the market for an aircraft of A350/787 size and yesterday's order, combined with the fact that the 787 is more suitable to short-medium haul routes than the A350 (which is intended as a long hauler) should favour the Boeing. It wouldn't surprise me to see the 787-10/747-8I pattern being continued in order major orders, such as CX and BA.