I've been playing a lot of survival games lately with inventory management and risk of items spoiling being a pretty key mechanic in it's core gameplay. I was kicking the idea around in my head of perishable items in FFXIV spoiling turning into either an end all product such as rot or a different kind of material for other unique recipes. Maybe it might give gathering and crafting another layer of depth along with giving things that players make more value because they are only temporary and need to be used within a certain amount of time. Maybe even extend that to gear where you can only repair it so many times before you have to replace it. At that point you could make repairs a little more costly by making them cost materials as well as gil to repair. Remove dark matter from npc vendors too. Would give more value to dark matter and other players being able to repair your gear. This is probably a terrible idea but something fun to think about.