That issue on the 737 being vastly inferior to the A320 family...

[GPWestjet]

Is the C-series poised to make a comeback? Maybe a stretched CS-500 seating 160-170? Theoretically, the C can be stretched to accomodate up to 170 passengers, possibly more. The DC-9 family featured a narrower fuselage, yet was stretched to seat 172.

I am Canadian so I am going to support Bombardier, but I don't think so.

Airbus is going to get orders from current airbus operators(mostly), Boeing is going to get current Boeing operators orders. and Bombardier is going to get whoever currently flies regionally and wants to expand, airlines that don't want to wait until Boeing makes there decision. Or for airlines that are not doing good(Losing money) that CAN'T wait until 2016/2017 for a better aircraft, the C series is available in 2013/2014, plus it is the ONLY airplane, all others are variants of there current models.

[Virgin Serbia]

Delta is about to commit to 100 737-9 to replace the 757-200s. Since they didn't order anything else, and they announced that they would order 200 planes in all, I suppose that means about 100 additional NEOs to replace the MD-88s. If they were to announce addiditional Boeings, they would most likely announce it in the same order.  

Just as we expected, Delta will also be a split.

The fast delivery time of the 737-9 was cited to be an important reason. The NEO is sold out through 2018.

Edit: It turns out that the order is not for the 737-9RE, but rather for the current 737-900ER. Delivery from 2013 to 2018.

Edit 2: Rumours say that the remainding 100 will be pitted between the Embraer E-195 and Bombardier C. The A320NEO vs 737RE choice will come at a later date. The 100 Cs or Es will not be a replacement for the MD-88. If true, this might be a replacement for some Delta Connection planes.

[GQfluffy]

I was about to uh...chide you on your "I suppose" but you edited it. Thanks. 

There's one problem with the 737 (other than fuselage width), and it all comes back to the landing gear length.

[Virgin Serbia]

There's one problem with the 737 (other than fuselage width), and it all comes back to the landing gear length.

Well, fuselage width is a rather minor one. Passengers hate it, but the more narrow fuselage should in theory also produce less drag. But a wider fuselage would surely help the 737RE a great deal. 

The main landing gear on the 737 is limited by the fact that it
a) can't be stretched, coz it in that case would hit the opposite L/G. They both fold inwards, towards each others. There is no more room to extend the gear further,

b) the swivel point of the gear can't be moved further out along the wing unless the wing box is heavily modified to take the stress during hard landings.

(The red line marks the center point)


Now imagine a wider fuselage. The center wing-box would be wider. This would allow for a longer landing-gear, while retaining the current wing-stress configuration.



In order to accomodate a 78 inch fan, the fuselage would need to be widened by 60 cm, thus giving a width of 436 cm. This would add 1 additional seat in each row, giving a 7-abreast fuselage. By comparison, the A320 is 395 cm, the C-919 will be 400, and the MS-21 will be slightly over 400 cm.

Advantages
More seats. Roughly giving the 737-700 a capacity of 172, the 737-800 - 220, the 737-900 - 250.
Better CASM (cost per average seat mile) than most competitors, if seating is maxed out.
Ability to fit more fuel tanks in the belly.
Ability to fit a larger cargo area in the belly, allowing for containers.

Downsides
It will not be an easy task to redesign a wider fuselage. It might be easier to build a new fuselage.
The nose gear will still need to be extended slightly.
Current rules don't permit passengers to be more than 2 seats (not including the one he is sitting in) from the aisle in case of emergency. A 7-abreast airliner would need 2 aisles, making it a 6-abreast 737 yet again. 
It would be heavy, and add more drag.
Range would probably take a hit as well.
Extra emergency exits needed on the 737-800.


A simpler sollution would be a 15 cm nose extension, and a 15 cm main extension, giving 30 cm wider fuselage. 406 cm is a bit easier to work with. This would match the MS-21 quite nicely. It wouldn't give the better cargo area though. On the up-side, the 737-900 wouldn't be such a tail-banger anymore.

[Virgin Serbia]

The Boeing board of directors have officially approved and launched the 737MAX

As expected, just a 737 with the tiny 66 inch fan. In order to solve the problematic noise that would have been caused by the smaller fan, 787-style chevrons have been fitted. These reportedly increase the fuel burn on the 787 by 1%. A revised tail section, and possibly a new APU is also shown in the official photos. Apart from that, it's pretty much a standard 737NG. It will only feature the CFM LEAP-1B

Boeing has received commitments for 496 planes so far.
 
See link for some standard Boeing PR department nonsense and some nice pictures: http://www.newairplane.com/737/737Max/#/characteristics