Every part of the Zodiac weapons seemed to be aimed to two goals:

-Make it last as long as possible.
-Use a piece of content that would benefit all players regardless of levels or that was being unused.

That second goal can be seen at all the stages of the relic so far.

- First we had to farm Fates of any level in almost every map. That (after the initial craze) has left the once unpopulated starting areas with people here and there doing fates so that new players dont feel like the world is empty.

- Then we had the books wich, again, made us kill random stuff, fates and leves and more importantly, dungeons. By making players redo old and low lvl dungeons it helps people who would otherwise have longuer queues for their story progression.

- The final step so far is the materia, this is the easiest one to understand. The materia system wich is more or less forgotten in the battle aspect of the game was suddenly boosted and not only for the super hard to obtain Tier IV materias. All of them were useful so, even low lvl players could benefit from it by selling their Tier I II materias.

So, for the next step, my bet is that it will either require Elemental materias (wich have absolutely no prupose in the game at the moment) or, what my FC and I have theorized, redo all the dungeons besides Coil and CT to get a random drop from the bosses for every one of them.