I don't think old events necessarily need new things added to them every time. Just like every other piece of content, it comes with certain rewards and you do the quests once and that's that. The only difference is that these have limited access.

That said, the issue with this event in particular is that it has exclusive character model pieces utilised for it (as I said before, Iroha's hair and spear) that are not made available to players.

Perhaps the game could take a leaf from the FFXV event's book and make those two items available at the Gold Saucer during the event, similar to Noctis's hair and mount?

Making the gear dyeable should just be a matter of them editing the gear model, not needing new items, although if they insist on making something new they could add upgrade tokens to the FATEs.