So what is the WAG on efficiencies WRT "clean sheet" narrow bodies?

Wiki says that Boeing says that the 787 will be 20% more efficient than the 767. If the 320 NEO is 15% more efficient than the current 320/73N, just how much more is there to get even if they cloned/scaled the 787 to 737 size?

Common fleet, quicker availability and fewer things to go wrong versus a true "clean sheet" are very significant advantages. Also, where will fuel be in the late 20 teens? All signs point to nowhere for crude to go but up on a multitude of fronts from currency devaluation to global demand to geo-political restrictions to self imposed carbon based wealth redistribution schemes to name a few. Can we afford to sit on the sidelines and pass up 15% in the hopes that yet another paperware/vaporware jet to be named later comes along...and for what...that additional 5%, maybe?

I would not count out the 320NEO, especially if waiting on Boeing to make one based on what they have said about it. The 320 NEO, IMHO, is a very strong contender.