Bah can't edit my earlier post on this mobile view. Too tired atm to make my own big ideas post but I will say my favorite thing from the OP is the labyrinthine deep dungeon design with in-duty story events. The materia to reduce vulnerability or weakness duration is also an interesting consideration.

Yo, can we make desynth less useless? They haven't added new types of demimateria since ARR. Give me a battle demi IV, master demi II, etc. Require those demis in useful crafting recipes. Could also bring back the convert option, but instead of converting gear into materia it will convert in something like an enhancement item for micro upgrades... +1, +2 your gear, can be sold on marketboard.

Weapons, it would be nice to customize glow color and effect type. I don't think 'relic' quests should be repeated for every job in the game. I would like to forge just one legendary weapon but it's an adaptable form-changing weapon suitable for all jobs. May require a cost to transform. May have special properties such as triggering certain enemies to drop some rare item when slain using a relic.