Just a thought that maybe the developers have discussed already. I don't know if this is the major problem still, but my understanding is that a major barrier to allowing characters to have more inventory space, bank space, creating player housing/warehouses/chests/whatever, etc. is that everything ever created, both characters and items, are kept in the database until they are deleted by the player through character deletion or selling to a vendor. What I propose is to have an archiving system that at the very least could delete long term, unused characters and items out of the database, but could be queried later to re-create them. I don't know the actual technical details of how the DDO database functions or all the various servers that are involved in running the game, but here's roughly how I envision this working.
For characters that have not been on in a long time, they are archived along with all their belongings. An XML file is created describing the character and all its possessions. The file is sent to a separate archive server and possibly compressed. If the player logs in, they see a special button to the left of that character that says something like "Come out of retirement". After pressing this, the archive server is queried and the re-creation process commences. Something like the 2D character creation screen is shown and an NPC commences a dialogue with the player while the process completes. If it fails for any reason, the NPC can tell the player that he has to talk to so and so and that he/she will be out of retirement soon, but to come visit the NPC from time to time to see how its going. This of course would initiate a trouble ticket in the background and a flag could be updated to have the NPC change replies when revisited to give an indication of the status of the ticket, possibly including the need to contact account support. Even if the process succeed, the player could log out for how ever long it takes to complete, but hopefully the NPC dialogue would last long enough to cover for it. It might even have some options where the player can be told about things that have changed since the character was last played, and an option to open the DDO store with a one time coupon to use in it as a returning player.
This system might also be used initially to offer players long term storage. A crate could be purchased that houses 10 or 20 or whatever number of items. Items are then placed in the crate. A label is attached to it. You tell the warehouse manager to ship it, and off it goes to the archive server. The warehouse manager NPC could then be asked at a later date to retrieve a crate with a specific label.