The cracks in the bulkhead (S) that have so far been found are in the lighter weight aluminium alloy that was developed to give a weight saving over the Titanium used in the A and C models.
I have not seen anyone taking about any new alloy to replace the one that has failed in a number of structures. I assume that if all the light weight aluminium was replaced by the original Titanium, that the plane would be overweight.
A bit of a quandary...