3G,
I don't think breakthrough is the word for it, it's more a continuous process of improvement. All the big engine makers are working on ways of making their products more efficient and less noxious and they do it all the time, like new combustion technology from GE, improved blades from RR. The airframers too are developing better techniques to get their planes to go further, winglets, composites, higher pressure hydraulics. So it's not just a powerplant issue, remember, these days the engine is just one bit of a system. If you want to switch an Rb211 for Trent you also have to deal with the impact on the airframe computers, maintenance logging systems etc. The cost of a retrofit is high, but a new build a/c will take advantage of the improvements - R-R's latest 211G/H-T has the T suffix because it has Trent core components, and later versions of the 747 are destined to have 'real' Trents together with improved avionics.
Long may it continue, it keeps is all in a job !
Vnv...
