WoW: UI Panel

Quote from Blizzard staff

• There were plans to make the backpack bigger, but the currency and pet changes in WotLK freed enough space and there isn't any plan to do it anymore. Still possible for the future though.
• There is going to be a dual-spec interface introduced in a content patch after the expansion. The talent spec process will be revisited at the same time. (Confirmation boxes to prevent misplaced talents, etc ...)
• The compatibility of TBC addons in WotLK shouldn't be too bad at the beginning. There wasn't any huge LUA change or anything like that.
• There isn't any plan to add class-specific elements like PallyPower in the default UI. Sometimes very popular addons might be integrated to the base UI but only when they fit general needs.
• There are no current plans to change the bag UI and make it just one large bag.
• A /castrandom command for the new Mounts/Minipets UI might be added to the game.
• Itemrack and ingame boss mods are still planned, but there is no ETA on them.
• The current implementation of the threat UI (% of threat of the main tank) in the beta is the final one. The point of the default UI is to be simple and very visual, for more detailed stats you'll have to rely on specific mods like Omen.