I know someone who works for Emirates at Zurich and she told me it's EK policy to only upgrade people when they absolutely have to (i.e. only when the flight is overbooked, and only at the last minute, after they know if anyone missed the flight, etc.) Emirates seems to be rather good at predicting loads (or bad at getting a full load, on some flights) so this situation does not happen often. Op-Ups are very rare on EK.