Maybe a dumb question but can’t you switch the engines to the more efficient ones? I mean it’s surely not cheap but maybe cheaper and faster than building whole new planes!?
The engines on the existing A380s will be replaced multiple times during their lifetimes and certainly those replacement engines will have some efficiency improvements. But I doubt it's possible to change the efficiency significantly without changing the diameter and or length of the engines. And that seems pretty unlikely given how many things you'd have to change and how much it would cost to re-certify, etc.