Based on my experience with other games, I think the crown store would benefit from the following items.
Backpack Upgrades (Single player and/or account wide)
Bank Space Upgrades
Mount Upgrades (Some, or all, of what the stable keepers offer. Either account wide- or character specific.)
Additional Character Slots - It would be nice to be able to play all the alliance\class combinations, and I and others I suspect, would be willing to pay for that privilege.
I came back during your welcome back weekend and quickly found out what a pain it is to have no space to store what you've gathered, and no money to buy the space. This leaves me with the options of either throwing away a bunch of stuff, making a bunch of alts just to hold stuff, buying gold from a seller (which can get you banned), just destroying\selling stuff, sending stuff to a trusted friend to be returned, or some combination of these.
None of these makes you any money. If you offered a reasonably priced alternative, you would be able to make money from people who need more sotrage space and are willing to pay you to acquire it immediately.