Case in point: consumables. Most players would probably agree that stocking up with ammunition and spell reagents feels like busy work that prevents them from diving into gameplay. I don't disagree with that. What's missing without it, however, is the flavor element. Consumables lend a touch of realism to the game world, plus a class- or role-specific twist to prepping for play. I need spell reagents before the raid, but my hunter buddy needs ammo -- and we both need food, but not the same kind. We're not interchangeable, and our consumable needs are a concrete reminder of that. I miss those dwindling differences.
I miss keys, too. Accessibility takes a hit when you have to have a particular something in your bags just to get inside wherever you want to go -- but without it, those places become simply one more click-and-port destination on the menu of easy access. Blizzard has to make it easy for new players and alts to whisk back into older content without fussing with details that don't represent the current thread of the game. UBRS and Karazhan keys, Aqual Quintessence ... Going back to re-check all the old checkboxes would be tiresome for contemporary players, indeed, but I still miss the business of needing to have all my stuff in order before I go.
Maybe there's a balance here to be struck, rather than sweeping the slate completely clean. Doing away with old keys that block current-era players certainly makes sense, for example. But does convenience always trump flavor? Are there some consumables, keys, or reagents you hope never go away? Do you find yourself clinging to the fading flavor of consumables, or have you already relegated that playstyle to the memory box?