Ultimate war was a 260 player map that was beta tested approximately 18 months ago. Sadly the sheer size of this map led to a lot of lag, due partly to server load and partly to the amount of processing power it took to display on the user's devices. As the map was largely unplayable in later stages when the unit counts grew it was discontinued.
The return of the listing to the search menu either is a bug, or signals that someone is working on the map and trying to improve it. I don't have any information either way. . .
