As time moves forward, so does WoW's built-in interface. Last patch we got some big additions in voice chat and guild banks (alright, that's not quite interface, but it's not quite gameplay either), as well as cursors and tracking for various types of objects and NPCs. There's not much in terms of interface news in patch 2.4, but Nethaera has just confirmed that a future patch will bring a big new feature: threat meters. (We first heard about this back at Blizzcon.)
Required by many raid groups, two big threat meter add-ons have been available for a while: KLHThreatMeter (a.k.a. KTM) and Omen Threat Meter. They both work very well (and Omen's new version is going to have some shiny new features), but they share a flaw: they don't have direct access to the game's threat info, relying instead on databases of clever deductions and discoveries painstakingly built up over months. This means whenever a new patch comes out, the developers have to figure out what, if anything, has changed in terms of threat numbers, and how much. Presumably, Blizzard's threat meter will have direct access to the numbers. And hopefully when the threat meter is added to the game there will me methods added to the API for accessing the numbers, so KTM and Omen can become even better alongside the new official meter.