From a followup post: “We already have some of the easily separable projects in separate repositories, like HPHP. If we could split our largest repos into multiple ones, that would help the scaling issue. However, the code in those repos is rather interdependent and we believe it’d hurt more than help to split it up, at least for the medium-term future. We derive a fair amount of benefit from the code sharing and keeping things together in a single repo, so it's not clear when it’d make sense to get more aggressive splitting things up.”