Not sure I agree with Singapore Joe's reasoning. Was offered the 'e-mail' upgrade for my most recent (19th Nov) round of flights on a BHX-DXB leg. I took the op-up. Y was certainly not full. However, there was also plenty of capacity in J. Last year I was e-mailed a similar op-up on a KUL-DXB leg. I didn't take it. Again, Y was not full.