I’ve seen a fair few other posts on requesting this feature, so I’ll skip the reasons and go straight to suggesting how it should be implemented.
I’d add a button to the player inventory bottom right to the left of the weight text area, that only appears while you’re at your main storage in your player house, and you have hit level 30 in any class.
The UI could be as simple as two input boxes, with the top box being level + overlevel selection (below this number, for example, if you input 30+0, my 30+0 gear would not be removed, but my 29 gear and below would be) and the bottom to be an input choice of cloth, leather, plate, weapon, all. The suggestions could be similar to bug report, so numbers on top of the keyboard, and at the bottom would be +1, +2, +3, +4, +5, Cloth, Plate, Leather, Armor, Weapons, All.
(this idea is severable)
The button won’t give shards right away, it’ll put them in a chest with 15 (or more) slots per page (one for plate, one for leather, etc.), so players can have a chance to recover their items before they have to contact the devs to return an accidentally broken down equipment. The chest could look like a recycling bin? If this idea were also implemented, the above mentioned button could also be placed here, in place of the Use Item / Breakdown Item button.
I am open to criticism, even if it’s not constructive.