I know some will disagree with me, but I don't think that pickle fork cracks are an argument for a new fleet. I think there's some confirmation bias going on here.
Cracked pickle forks are a design defect. And, design defects can effect brand new planes (787 batteries, A380 wingspars, 737MAX MCAS and the PW-powered A320neo engines...). Hell, based on recent years, design defects are more likely to affect new planes.
If QF had already started its NB replacement program, there's a pretty good chance that most of their fleet would be grounded or flying with limits. To the extent that anyone wants to rely on design defects as an argument about whether or not QF should replace it's fleet, I'd say that QF being a late adopter has allowed it to dodge a stack of bullets lately.