I am not quite sure what to call it yet, but it involves capturing locations, like in Day of Defeat, as well as capturing the flag.. Here is my idea:

It starts with one Build Phase, and then one long combat phase that lasts until the end of the match. People will have to use blocks and panels that are already on the map, and in order to capture a location or flag, it has to be adjacent to another location that has already been captured, and the first location to be captured for either team always has to be adjacent to their HQ. The Combat Phase will have people using objects to defend bases and locations, but none of the objects are indestructable, and it will be the engineers doing the work. At captured locations, objects and vehicles will spawn nearby. Think Onslaught from Unreal Tournament 2004, but with Flags and Strategic Points instead of Powernodes and Powercores.