I'm not sure whether the current difficulty in moving items between characters in the same account ("alts") is 1) a game-design decision (to forestall certain exploits that might be possible otherwise) or 2) a result of performance considerations or memory space limitations.

But if it is #2, then perhaps we could make moving stuff between alts easier by allowing sharing of one or more retainers. Here, you would hire a retainer nicknamed "Ret" on one character in the account, and then hire "Ret" from another character in the account as well. An additional menu entry at the Retainer Vocate, "Hire an existing retainer of this account," would be added, which when selected would ask for the retainer's nickname.

In the software, this might be implemented by simply having two pointers (one for each alt) pointing to the same retainer data structure. There should be no increase in memory use, no increase in the amount of data that needs to be loaded, no performance decrease.

There might be some necessary restrictions on a shared retainer, such as not allowing bound gear to be stored in that retainer, and you might not be able to equip it for ventures either, to prevent transfer of bound gear between characters. I'd be OK with that on one retainer.

Of course, there might not be much benefit to SE in doing this. I'm not sure how many people play alts, or how many would do so if it was easier to transfer stuff between them, or whether that would increase SE revenues.