It Back when there was no sticker book and no option to use transmutation stones to recreate a piece of equipment, I would've agreed.
But these days it is really comfortable to organise inventory. Well, at least for me with my 12 character non ESO+ account. There are just a couple of habits that one needs to cultivate and there will never be any inventory bloat.
1) Know your build's gear. Don't experiment, that's what the PTS is for.
2) Use the sticker book, don't hoard gear. With 1500 transmute crystals it is possible to make 60 pieces of gear at once. That is 5 characters!
3) Get all the free storage space. Bank (240), Inventory (200 per character, 10 characters are free), Storage Chests (360).
4) Use motives, plans and recipes when you get them. Sell them at once, if you know them.
5) Use up your consumable materiels. Craft potions, glyphs and food to sell them on guild stores. The good ones sell like candy. The others mostly sell as raw mats for good gold. Only the provisioning mats that are not used for commonly used food and for daily crafting writs need to be sold to regular merchants, 5 gold apiece.
6) Use Houses for storing furnishings, not the bank.
7) Hoarding is bad for mental health. Sell like crazy! Use Master Merchant or Tamriel Trade Centre to know real value and fill up all of your 30 slots in every one of your guilds.
Remember: The bank inventory is limited to 240 slots, but the amount of gold is limited to 2.1 billion.
There is more, ofc. But these are the most important.
I think it could be anything, but players would probably choose things they can no longer get in game, or other sentimental items. I would turn "Darien's Promise" into a collectible.