By the time Boeing starts the next clean sheet there will be nobody with the old experience left and nobody who already developed, designed and certified a new aircraft. It's derivatives, damage control and repaying their loans how they spend their money. If they get the 787 line up and running again with no more hickups that's at least one good program. The MAX might carry on, however I am not sure about 7 and 10. Will EASA agree to another grandfathering? And the 777X will take years to be through certification.
They should invest in some midsized model above the A321neo and prepare to launch the 737 follow on family. They must do it right the first time.