I am unsure if this is additional apron staff placed on these flights (lower cost) or if the shower areas are not being used heavily (on the ULH 15-16 hr flights). I can confirm I see them seated in a passenger chair when required and the uniform is very different as already noted. I think a shorter LON-DXB flight will perhaps more consistent shower usage while I could see many unused hours on the US flights.
I think most of us agree that EK is hurting on the ULH flights when it is heavy Economy bookings and really depend on that Premium revenue. With limited success, they have tried to raise the price charged, but with EY and QR (and others in certain US markets like SV or RJ), it has not been sticking.