I've thought about this a lot, and these are the things that would most improve the DDO UI for me:

1. Let me create a list, as a file, of the contents of any given bag, or of my inventory, or my bank. It needn't have anything save the names of the items.
2. Let me choose to stream my chat windows to files on my hard drive. Names could be redacted if deemed necessary, but there's often content I'd prefer to be able to reference at a later date.
3. Let me access my alternate character's inventories and banks, even if read-only, from inside the one I'm currently logged into.
4. Let me name my bags! Character limits would be fine, but figuring out which huge back is shroud, or epic ings, etc., is a royal pain in the neck.
5. Let me make various items different colors than the default ones. For instance, belts. My wizard has 7 amrath belts on a hotbar (both of the wizard ones, all four of the savant ones, and the wild mage one) for mixing and matching the clickies. Why shouldn't I be able to customize their color? It would be a local setting, wouldn't need to be transmitted to the servers even (the same is true for most of the above suggestions).

The only one that appears to be technically challenging to me is #3; the others are mostly to do with handling text output (which my C++ students learned in the first week of the semester).