Facebook's answer was "fine, we'll build our own routers" (in the datacenter, which is where quantity comes in, and is now v6-only (with few exceptions): https://www.internetsociety.org/resources/deploy360/2014/cas...

Major tech companies have constraints, but when they decide to move, they can move almost anything. It would be cool to see how constraints and problem solving approaches differed among the FANG companies as they grappled with these issues.