On a good day, I'd say that Warcraft 4 is a game that's going to get made at some point in the next decade. On any other day however—and this is one of those days—I'd say that the game is never getting made because Blizzard's too engrossed with MMORPGs.
Needless to say, despite how unlikely it'll ever get made, Warcraft 4 remains high on the list of every PC gamer's list of "most wanted" titles. To that end, a gamer—Steven Luo of the TeamLiquid forums—has created his own Warcraft RTS using World of Warcraft assets and embedding them into Starcraft 2. He calls it Warcraft Alliance and Horde, or "WAH".
More than just a simple map, WAH is a fully implemented RTS game mod with models, textures and sounds referenced by expandable melee maps.
Here's what it features, according to Steven:
1. 2 factions: Alliance and Horde, 14 buildings, 16 units and 18 heroes and over 50 creeps.
2. 3 melee maps right now: Lost Temple which made in Bloodelf Style, Crossroads that copied from WOW and Ashenvale that full of Nightelf style. New melee maps could be added smoothly on the framework.
3. Complete AI system for skirmish act as players.
4. Many WOW features, regions, units and abilities are implemented in the RTS game. You can see Undead Rogue or Bloodelf Paladin which is in early WOW times, and also can find Pandaren Monk, Leishen, Malkorok that in recent WOW version.
To play the game, just hit the Arcade of the US, Euro, Korean or CN in Starcraft 2 and search for "WAH" to enjoy a WAH melee map. The game mod weighs in at 245 megabytes, so it'll take awhile to download. But once you have the assets loaded, every other map will only take 5mb.
Further details of the mod can be found at ModDB.