Originally Posted by
Aihkio
At their present level computers still cannot design anything even close to the complexity level of an airliner.
Much less eliminate the possibility of unanticipated fatigue cracks, which may relate the the interaction of design and fabrication techniques.
Of course, larger engines and increased weights on an old-design airframe can expose new issues. But if anything, that seems less likely to happen than with a wholly new design (assuming the appropriate analysis is done when the upgrades are made, of course). There are lots of possible advantages to starting with a clean slate, but this doesn't seem like one of them.