Out of interest TDracer why do Boeing keep kicking the 737 can down the road? Why not build a new aeroplane or resurrect the 757? It seems ridiculous to have a 200+ seats on a 737 airframe.
That's what Boeing really wanted to do - once they had the 787 under control, the plan was to create a completely new aircraft to replace the 737. But then Airbus launched the A320 NEO and it sold like the proverbial hotcakes. A completely new 737 replacement wouldn't have been ready until nearly 2020, then take several more years to get up to the ~50-60/month production rates currently envisioned for both the MAX and the NEO. Conceding a several thousand aircraft market to Airbus while developing a 737 replacement simply wasn't an acceptable option.
Resurrecting the 757 isn't an option - the tooling is long gone, plus it would still need a new engine to be competitive.
A 737-10 - if it happens - would be a stopgap until the new midmarket aircraft would be available sometime in the mid 2020's.
What that MMA will look like is still pretty fluid, but expect something with capabilities along the line of the early 767s. In fact, my personal idea for the MMA is basically a 767X - 767 cross section with new engines and a composite wing. When you're talking 200+ passengers you really need a twin aisle to keep turn times reasonable (sit near the back of a 757-300 some time and time how long it takes to get off the aircraft after you're at the gate
).