There have been numerous quality of life improvements to World of Warcraft over the years. From heirlooms, to Looking for Dungeon and AOE-looting, Blizzard does a pretty good job of cutting out the unnecessary or improving on older systems to make our gameplay experience go much more smoothly. Which makes me wonder just when we'll get some sort of account-wide storage. I'm seeing it as a physical location in-game, like your banker, where players could dump gear and other vanity items. Other characters on your account---Horde or Alliance, off-server or not--- would have access to the storage.
It'd look like this: you're running a heroic dungeon on your shaman and you roll greed on a pair of cloth gloves that dropped from that last boss. OMG you win! Back in Orgrimmar after the dungeon run is complete, you're about the vendor the gloves when you remember "Oh yeah! My baby warlock could totally use these gloves (for xmog, as an upgrade---whatever). I'm going to head over to the account storage NPC and drop these in and retrieve them on my 'lock the next time I log on!" Boom. You don't need the gold anyway, and now your alt can benefit from the time you've just spent in-game.
And then when you happen to come across a Fishing Chair in an Unclaimed Black Market Container, it won't sit unused on a character you barely play. Really, it could work almost the same as your chest in Diablo III, for those familiar with that title, except that perhaps in WoW's version any items placed in storage would become soulbound if they weren't already---seems there might be potential for auction house abuse otherwise. There's also the unresolved issue of players rolling need on an item for their alts when in random dungeons, though Blizzard could make it so that players can only greed on items that are not main spec, or are of a different armor type to avoid negate that issue.
I don't think there's any question that account-wide storage would be used. Is it time?