The problem here is that what Boeing is selling ("737 that spends significantly less fuel and doesn't need recertification") simply can't be made safe. Whatever

The problem here is that what Boeing is selling ("737 that spends significantly less fuel and doesn't need recertification") simply can't be made safe. Whatever results from the marketing driven goal (selling something that doesn't and can't exist in reality) will remain unsafe as long as all the "already sold features" are preserved. So it's not if they should "start from clean" but just accept the need for the new certification and then do the changes that are really needed. It will be less profitable for Boeing but it righly should be this time! They are killing people otherwise.