Wouldn’t QF just give the 747 pilots the new spots on the 787 and vacant spots on the other fleets?
Only if it were somehow negotiated that ex 744 pilots would fly the 787 at 744 rates - and that ain't gunna happen.
A move from the 744 to the 787 would be a reasonable pay cut and thus most 744 pilots will be looking to minimise their pay hit when the move eventually has to be made.
The RIN process in some ways, allows this to happen; certainly for the more senior.