Since most items are bound to character why not have a vault system. Vault systems are implemented by other MMOs I won't mention which since I am not here to promote them but they work.
Have a library of all the items a character can unlock like a library/vault and you can just equip the items from there
No more duplicates triplicates and so on, no more massive storage for vendor, you can even have consumables go to your library where it keeps track of them, with the library being either character or account or mixed.
I imagine it will spare everyone from having a string of code for each item that has to be remembered in the database and instead you have it as a global library of yes u have it unlocked or locked

The gemstone system can be utilized in some other way or as an attachment to it. Honestly with some MMOs just allowing you to pull the item form the library into your inventory its about good enough to spare everyone so much storage.

And don't worry, you can still sell library storage and inventory storage