Yep, but from what I also read, their might be a limitation. From his words: "The game support multiple collison files, but currently I can not edit the list file for them (navmesh textasset in the Map list file), but I don't know how the game will handle another collison file, so for now we can only leach from the vanilla one until they release the DLC map to see how they do it."
Now, I'm not advanced with this stuff, but what I think this means in simpler terms: In his clip, he had to use the Cafe as a "gateway" to visit the AA2 school. I'm not saying, you have to go to the Cafe every time to get there, as it was just a "Test". I'm saying, he cannot manually just add the AA2 Map anywhere on the map. It has to be branched onto another vanilla location in-game. This is why he needs to wait until the DLC Map is released, so he could import a new area, without having to use a vanilla location as a gateway. Now once again, "I could be extremely wrong here". This is just my guess from using context clues and watching his clip. Maybe someone with knowledge, or Dark could correct me on this.