No information, already announced in previous live letter that materia system will be reviewed.

We can speculate as much as we want.
@Remus : maybe once your End game gear reaches 100% spiritbond you will have the option to attach a materia. then it resets and you have to spirit bond again to 100 % for another

One fun thing would be resistance materia allowed on Endgame gear. Prices would skyrocket