I'm not sure if this has ever been suggested before but the idea popped into my head recently.
As you are aware Inventory space is limited to a cap of 80 on everything as far as we know, be it your Mogsafe, Mogsatchel, Mogsafe, storage, and Moglocker etc.
But there is another storage space that we have that isn't really mentioned and that is the space reserved for your Temporary Items for Abyssea, Campaign Battles, and other various events that use temp items. Now I think that it is logical to assume that this space also has a potential capacity for 80 items also although it never really gets that high. I think I have 15-20+ temp items for Abyssea which still leaves substantial room if indeed it's capable of 80 items. Since your Abyssea temp items are stored that inventory seems permanent unlike the temps from other areas. They are most likely independant of each other.
This is my Idea. In order to help ease the 80 cap Inventory space of the inventory for your gear, when you change jobs and go to the storage NPC's for your Artifact Gear, or your Relic Gear assuming you have the complete sets and the appropriate storage slips. Why not have the NPC give you an item that works sort of like the magian spectacles where you have infinite uses called "Insert Artifact or Relic armor Name here" armor set that when you use it, it deposits your Artifact gear and or your Relic gear into the Temporary Item storage area where you are free to equip it as long as you dont zone, zoning requires you to use the item again and when you change jobs you just give the item back to the storage npc.
Seems to me that this would help ease inventory issues for some people that still use pieces of Artifact and Relic gear in their macros.