DECs "the worst decision ever" I doubt those who took the jobs or EK agree with you there!
All of the accelerated and DEC options remain in play, but EK will only use them if they run out of qualified more senior F/Os on a particular fleet. If you are not on that fleet at the time then command transition upgrade of F/Os or fleet transfers of Captains will take place. If you are on the fleet that runs out of F/Os then you will be in luck but not before. This is what is currently occurring within EK but is no guarantee of the future. EK will do what is best for them as they see it not what the unlucky fleet pilots who get bypassed for a while may want. It is not a system that is fair to each individual pilot but it does keep the aircraft flying, the airline expanding and the profits rolling in. Which ultimately ensures us all of a secure job with career progression.
If they stuck to strict seniority for upgrades I doubt they could recruit enough pilots to cover the cross training required and extra time on type prior to checkout.
They rely on those bypassed to carry the burden of their poor planning and the fluctuations of aircraft deliveries which is unfair. These guys understandably suffer from poor moral and considerable anxiety because of it. I think EK could do a lot more to compensate these guys if it fails to solve the crewing issues. Paying them some form of bypass pay to let them know that the company values them sticking around to become Captains for EK would go a long way to reducing the bitterness.