With the upcoming emphasis on warehouse usage (because carts and containers will be lootable on red worlds) I think it's important to add a feature to help us organize warehouse contents: tabs.
Warehouses could have, say, 4 tabs. They can be named.
Each tab shares total warehouse space. They are purely for helping organize.
Ideally this needs to be a serverside feature (not a client mod) because if I create a tab called "Chainmail" and put all the chain armor in there then my guild should see the same thing.
Programmatically this should be pretty simple: warehouse items get a new field to state which tab they are in (0-3, with 0 being default) and tab selection simply hides whatever is not in that tab.
Bonus points: Number of tabs is configurable.