Boeing won't reconsider a new design.
- For the 777, they won't build an advanced replacement.
- For the 747-400, the 777 is the replacement.
- For the 747-8, it's just a low-selling competitor to the A380.
- For the 767, the 787 is the replacement.
- Finally, for the 757, the 737-9 MAX is the replacement.
That leaves the "old technology" 737 MAX and 777, and the "new technology" 787. Period. They'll phase-out the 747-400.
While Boeing builds the 737 MAX for the next 20 years, they are NOT going to build a replacement for it at the same time! The 737 MAX is here to stay for decades.
The big question, then, is why did Boeing develop all this 787-based technology, with no intent to use it on development of further airplanes? It would appear that Boeing's going to build the 777 and 737 MAX lines till kingdom-come, with the 787 line as a sole, separate technology. With the 737 MAX decision, they have no new airplanes with which to use the 787 technology on!