Keeping your options open
I wonder if pitching this as the 'replacement' of the A320 or B737 sets the right tone.
Looking out 20 years, it's quite likely that Airbus and Boeing will not replace the A320 and B737, respectively, on a like-for-like basis. If Airbus and Boeing believe their own projections for traffic growth, it's not clear that one aircraft type could or should replace the A320 or B737, in my view.
On the engine side, there could be opportunities for several engine manufacturers and several types of engine technology.
Meantime, the A320 NEO looks like a very good strategy for Airbus to pursue, regardless of whether it's quite as good or slightly better than the B737.