From the horses mouth, the article states:
Vic Sheppard, vice president of Emirates in the UK and Ireland, said: “We’ve seen some of our best-ever figures for a UK route launch, despite operating through some tough times. We would certainly aspire to graduate to a 777 here. That would be a natural progression for us, and not that ambitious. We would expect that after maybe three years."
Could be brought forward once all those Arabs come to invest in the Toon...