Boeing did an all-new 787. That didn't work out particularly smoothly either.
Regarding grandfathering of certificates and qualifications, we've discussed the PowerPoint training and penalties for additional training needs, but a comment by a US 737 crew on, having done the computer review, they were unexpectedly presented with a Max for the first time, both of them, due to a rescheduling, was revealing. They said they both felt quite unprepared for all the differences, and although they completed the flight straightforwardly, said it would have been a different matter if anything had gone wrong. THis really comes down to commonsense not just at the manufacturer or the FAA, but the airline as well, with not even thinking of this as an issue. As well as Boeing engineers being sidelined, it's aviation pros in the airline management structure as well. Did nobody think to give their captains a hundred hours or so on the Max before putting them with an FO doing a first run ?
I don't seriously expext the Max back in the air before 2020, at least. I'm wondering when the Boeing stock price "Emperor has no Clothes" situation will finally get recognised. Because only then will some management changes swiftly follow. I think the balloon will burst when the production line has to be stopped.