Functionally it wouldn't make sense for r/e/re gear to be converted to materia, because that would counterattack the reason the devs made it r/e/re in the first place, which was to get people who already have it OUT of the queue to get the item.

Nothing changed about leaping lizzy for 5 years and it was camped to hell. Yet change one little sign on the equipment and within a half year Leaping Lizzy roams free. Nothing about the supply or demand of leaping boots changed...except the people who were allowed to squat it and monopolize its distribution.

If you make seer's cowl materia'able and have it turn into a significant materia...it will be camped so hard Russians will show up at your door and break your knees if you so much as try to enter Mun Tuy.