All the above assumptions would work if EK upgraded on next in line basis. History shows this is not the case. It is done by fleet.
Net 777 fleet growth is said to be between 30 and 40 from now until 2020 (It was reported as 160 but think that has grown because of the extra 77Fs. All classic 777s gone with first ER retired in 2017). There are 80 380s on the way in the same time frame, with remainder of the 330/340 to be retired. So about a 25% increase in the Boeing and bit of a doubling of the Bus fleet.
So the top 25 to 30% of 777 FOs will be upgraded by 2020, and all current Bus FOs will be upgraded. If/when the 350s arrives could tilt this a bit more.
Out of seniority commands will continue.
The Don