I'll second the gear guarantee, so long as we add the option of having gear not better than our currently equipped gear go to our inventory instead of our armory chest.
That said, to double up on reducing inventory waste, I'd also like to have all gear that is merely a recolor of another piece from the same dungeon be consolidated into one pieces with conditional stats (mostly in terms of Defense/M. Defense), usable by jobs of any of those roles, and try to rotate those consolidations around a bit (e.g., Aiming/Scouting & Striking/Maiming; Fending/Maiming & Striking/Scouting, Aiming/Casting & Scouting/Striking/Maiming...).
And, to that same end, I'd also like to see totems and tokens moved to the Currency Tab and perhaps even to eventually rehaul Materia to take up no room in our bags. Ideally, I'd change it into a granular currency of type (without grade, that being determined instead only by how much you put in) that is used only to change gear stats from one to another, reducing its need and removing its inventory costs. In that way it improves stat-customizability without necessarily adding steps beyond gear acquisition and greatly reduces inventory bloat.
Aside: On that note, in a distant future, if not the next FF MMO instead, would greatly increase potential job versatility and have jobs again use all primary stats to at least some degree with playstyles varied by stat balance and role determined almost equally by one's stats (so that if one has a full set of Mind gear from their WHM, they could pass that down to their MNK and play said MNK supportively, too, even if with a far lower maximum HPS), give some degree of stat cost to additional Defense and rehaul gear to actually be a collection of parts elements that are separately removable (so that you can trim down Fending gear to Maiming, Maiming to Aiming or Striking, Striking/Aiming to Scouting, etc., or vice versa), each of which would adds to some stat while reducing another. I.e., you'd have crafting actually allow for near-bespoke visible combinations of parts, making it far more interesting, while also reducing the inventory space required for omni-leveling. But that'd be a thing of pipedreams, obviously.