Re: Poor Design
Are yes, the passing of Properly Built Kit, something to mourn indeed.
Though with aircraft, the limiting factor is primarily fatigue life. Commercial airliners have to be built strong otherwise they'd be useless in service. There's A320s and 737s with way more cycles on them than this 747; they're strong. They're often stronger than military aircraft, which tend to do far less flying.
With 787 and A350, carbon fibre is the primary construction material. Provided it's not abused, this looks like it will last forever. Quite literally. No fatigue. Airlines buying these today will likely never replace them (at least not until something radically better comes along). Upgrades, refurbs, certainly but the airframes themselves should last forever. Boeing and Airbus are building aircraft that will mean they're not building so many in 20 years time.
Today's 787s and A350s will. Scone our grandkid's older-than-us engineering marvels.