NSNB
Since you asked for thoughts. I have a few. This is my personal thoughts and are not rumors just what I think to be common sense or based of things I have heard Munoz, Kirby, Or Levi say:
1) when asked on the 3qt call about RJ's Scott Kirby used a phrase I had not heard before:scope maximum. That was the limiting factor in more RJ's. 65 737 took United total RJ needs to ~350 (that was from June timeframe before the "new team". Currently they have reached the 255 big RJ limit (orders plus actual aircraft flying). If they want more big RJ's the only path forward under the UPA is a NSNB. I believe that the 190 is in our future. Why? Because United already owns several 175 and an order for the 190 can be package together with a 175 order (total big RJ's if we get a NSNB is 325)....greater number of aircraft in the order should yield a better price. We also have contract maintenance set up in every city where the 175 flys so in short order you can deploy the aircraft with technicians ready to work on the airplanes.
2) if they do a NSNB then we have a fleet of aging 737/320/319 to replace. That is a total of ~450 airplanes. The oldest 737 and 320 will be 30 years old in the next 5 years....why not replace them with a more efficient technology.
3). I honestly believe that in the short term you will see a large (~25) number of used 320 being purchased. If they really do have slack in the current system and can get 25 used 320 series aircraft, plus 4 737-800 plus the other 6 used airbus from china they have enough lift to cover replacing most of the 50 seat RJ retirements. Assuming these airplanes are the same vintage as the Chinese 319 you can then retire some of the oldest 320/737 aircraft after the first of the SNB arrive.
4) Current generation aircraft prices are going to start to decline with the introduction of the NeO/Max/E2/CS. Airlines will also take these new aircraft and put older 320/737 up for sale or not renew leases. It should be a buyers market. Might be a cheap time to buy used aircraft. (That's what I gather from Levi comments on cap ex)