How much more efficiency can be wrung out of the jet engine - technology which is over 70 years old?
Around 0.7m (over 2 ft) bigger fan than the biggest Trent.
Intriguing to see a return to the carbon fibre blades originally developed for the early RB-211, but abandoned due to a tendency to fail under birdstrike and similar impact. I guess the heavy titanium leading edge of the ultrafan must have something to do with that.
I would assume that carbon composite technology and manufacturing techniques have advanced somewhat in the 50 years since the RB.211 fan blade was developed, also, I'm sure Rolls Royce has studied the GE90 fan blade . . .