Boeing has stated that the future 737 replacement will be based on 7E7 technology.
However, the Delta/American MD
-80 replacemet you talk about is likely to go to the 737NG. The 737 will be in production for quite a few years down the line--Large backlog already, US military just ordered it as a P-3 replacement (other militaries are likely to follow), WN
and other LoCos are still growing at a healthy rate, and of course the hundreds of MD
-80s that need to be replaced.
"Millions long for immortality who do not know what to do with themselves on a rainy Sunday afternoon"