If I was on the flight in Y, I'd be hopeful of an opup depending on which route it was.

Things I would interpret - its a 2 class plane (then you knew that looking at the seat map etc)

Y is already oversold but EK are willing to sell 2 more Y seats factoring in space in J for op ups and the liklihood of cancellations/missed connections.

It is highly likely that flight will go out at 100% capacity.

I would look at the seat map (as a rough guide for the space left in J) to determine the amount left or go onto the EK booking engine and do some dummy bookings....