Part of the point I'm making is that an out-of-order format is more efficient because we can send stuff as it's ready (so footer can go as soon as it's ready).

Part of the point I'm making is that an out-of-order format is more efficient because we can send stuff as it's ready (so footer can go as soon as it's ready). It'll still "slot in" the right place in the UI. What this lets us do, compared to traditional top-down streaming, is to progressively reveal inner parts of the UI as more stuff loads.