The game can be patched to be able to read the new stuff, like the new Megas. However, the danger then comes in the update being applied, the new stuff being obtainable in X/Y, and the update data being deleted. What then? You can do that now, deleting the updates, and the Lumiose Save Bug™ returns. So, if there is an update, DO NOT delete it or you may bug your game if you, say, trade the Sablite or whatever it's called and then remove the update. The item may just vanish in your bag or from a Sableye's hands and it's like it ceases to exist. Reapplying the update after handing Sableye another item may cause conflicts. So don't delete the update, as Nintendo would likely presume you are not going and deleting that, but some could do it by accident.