737 sales inflation

Recent weeks saw an inflationary order boom of Boeing's 737. 30, 40, 50 at a time, Unidentified Customers mostly. Boeing has sold 446 of the 737 so far this year, with only 14 cancellations. Book-to-bill ratio is well above 1. If you take the already announced production rates into account, production now would run until mid 2016 without any further orders.
Airbus does not have this sales fortune with their A320 family so far this year - 221 sales is not bad, of course, but book-to-bill is clearly below 1. Still, without any further orders and with announced production rates, the last A320 family aircraft would leave the factory in mid 2016.
But what could be behind the recent sales success of the Boeing 737? Here is my (2 cents worth) theory:
Boeing tries to drive Airbus into the -NEO by selling the 737 at huge discounts and then outperforming the A320NEO with a new aircraft.
If you followed the conference call on Boeing's 3rd quarter results, you can guess that Boeing decided not to reengine and to develop a 737 successor for the 2020 time frame. Whether Airbus believes that this successor will be significantly better than the A320NEO will probably trigger the decision pro or contra the -NEO.
If Airbus believes that in the early 20's there is not much more technology out there than today, then Airbus will go forward with reengining (or is it reengineing?). But if Airbus fears an overwhelming superior competitor coming out of that development, then Airbus will forego the -NEO idea.
So what technology could be there ready for EIS in the early 2020's - meaning that it is available (TechnologyReadyLevel6 for techies) in 2016 at the latest? Enginewise: not much more than today I would say. Rereading an article from AviationWeek it is even questionable if all the engine technology for the -NEO would be there in 2016, as the article suggests that the LEAP-X1C for the C919 does not feature all the technology CFM officially claims it has on hands - if that is true, then this would also be true for the potential CFM offering for the A320NEO and the 737RE - and maybe that is the reason why Boeing kind of backs aways from the -RE story. Combined with the well-known problems for installing the larger engine under the wing of the 737, the LEAP-X would not get to the same SFC level than the larger fan-GTF (81", as Airbus revealed at the ISTAT conference) for the A320.
So, if the differentiation between a A320NEO can't come from the engine, it has to come from the aircraft itself. What is possible? A carbon-fibre fuselage, of course. Although, a recent posting from AirInsight suggests that maybe Aluminium-Lithium could be the material of choice for future high-cycle aircraft - just look at the Bombardier CSeries.
Anyway, significant weight savings could come from a new material. But then I guess everybody expects the fuselage to be wider than today's 737, at least matching the A320 in cabin comfort - meaning, that a portion of the weight savings is eaten up by the larger fuselage diameter.
A few years ago Boeing scrapped their 737RS studies. I talked to a Boeing Technical Fellow not long after that announcement and he told me that one of the reasons was that they did not found enough weight savings back then. As today's 737NG is still build upon the certification of the very first 737, Boeing did not have to take care for some (weight costly) security measures that you have to build into an airplane if you want to certify it today. The Boeing Fellow expected the extra weight you have to put into the aircraft at 10,000lbs, if I remember correctly. So Boeing would have to find 10,000lbs weight savings to be where they are today...
The wing is another area to improve the efficiency of an aircraft. Here chances to see carbon-fibre is better than for the fuselage. Lower weight and better aerodynamics could lead to a few percentage points in improvement.
Another way to improve efficiency is to enlarge the aircraft, as this article suggests (of course this works out for the airline only when they can fill the aircraft).
Undoubtly, the trend goes to larger aircraft and there is no replacement for the ca. 1000 757's on the horizon so far. So both next generation narrowbody families from Airbus and Boeing will cover the 757 - at least in passenger capacity, not necessarily in range.
So, what is my verdict on the -NEO question? Don't know, but we all should know by December 31.
Until then we can all have fun with speculating, just as I did here.