There isn't a single city in the country which currently has a separate board for its suburbs. Of course, that doesn't mean it's a bad idea. However, if this is done for Philadelphia, it should also be done for Chicago, at a minimum. Even though the posts about the suburbs are a small minority on that board, people looking for info in the suburbs are rarely interested in the city, and vice versa.
Also, New York City needs to have separate boards for its suburbs to split them off from the rest of New York State. Which has been the subject of numerous discussions here.