A few years away yet?
I have no idea if either GTF or the open blade approach will live up to their manufacturer's claims, only time will tell. Imagine for a minute though that they do deliver 15% fuel improvements, how long will it be before any of the airlines can afford them?
Bear with me here-
From a quick scan of the net (and some very rough calculations) I see that a brand new RR Trent 1000 (which seems to be a decent, modern turbofan) costs something like 30 million US dollars. I got this number by taking 2.6 billion US dollars and dividing it by 86, the number of engines Virgin Atlantic are getting in a deal that was signed just a few months ago. Now those are for brand new planes, I believe they are for Boeing 787s, but how often do the airlines upgrade their fleets?
If you did want to fit 4 brand new engines to an existing aircraft then how long will it take you to pay back that 120 million US dollars (and that's presuming they cost the same as the current tech, which I seriously doubt will be the case) from the 15% fuel savings? Those planes are not going to be refitted in 5 minutes either. I guess that comes down to how much the fuel costs. Also, where do you get the money to buy those engines in the first place if business isn't that good? As someone pointed out earlier, airlines like BA are pretty strapped for cash right now.
Will be interesting to see how long it is before we see any aircraft with either of these engine technologies.