d to do with the thermal protection
scheme for BFS/Starship. The nice thing about metal is that it conducts
heat better than a carbon fiber composite would. That might be an
advantage during reentry.

Heat capacity or thermal resilience is certainly an issue.
Another is the ability to use the tanks as a hull when
pressurized. Metal hulls can be possibly reduced in thickness
to compete with composites. At a certain point thermal
properties of metal may make metal superior.

If Musk has only a fuselage material as the change then
my comment does not apply.