My proposal: Make the Vault like a Kiosk. You collect the gear and can match it into your vault, almost like that book as a kid where you tried to get all 50 state quarters. Then you could have "Miscellaneous" Vault space, for gear that doesn't fit under the "Raid" or "Iron Banner" sections (just examples). I would find this to be the best way to revamp the vault and make it fun to collect gear again. You can still separate Weapons and Armor, but make it matchable and if you are really feeling lucky, maybe a Record Book type activity for collecting, and Rank up your vault for more "Miscellaneous" space and cosmetics.