It's actually much scarier than that.
I will not be deciding how it works together, I think that should be the duty of the level creator. I will, of course, offer any counsel the person needs, and maybe a little prodding.
It might even be that the designers who have adjoining sections of the city might add tales (text events or tavern tales) about the areas around them. You now, something like, "Most decent folk in these parts steer clear of the Scifer section of town. I been there once and it's full of all kinds of weird looking buildings and odd contraptions. I wouldn't trust someone from the Scifer section for a second." Please note that this example sets up that there may be incongruities between the two areas, while at the same time promoting the other area as a place of intrigue, which will surely cause the PCs to visit at least once.
We are respectful human beings in this community, so I don't expect anyone will disrespect their fellow designers. If by some weird circumstance that does occur, we can deal with that then. A major goal of this project is to get us talking with each other.
So, maybe someone announces that they want to do a sci-fi section and someone else hates the idea, we should be able to work out a compromise, like maybe there are sci-fi elements, or maybe just inside the Ward limits are teleporters to a strange city within the city, or maybe there are sci-fi items, but explained in fantasy terms such as some of the early AD&D mods. (I'm doing a fantasy section by the way, with no sci-fi or termite hill elements.
)