Stabilised != final though, so you'll still need a layer in order to find all of the new knowledge and compare it against what everyone has locally (not going t

Stabilised != final though, so you'll still need a layer in order to find all of the new knowledge and compare it against what everyone has locally (not going to download 50GB every time someone posts a new useful SO answer), and update the local store. Why not keep that index centrally for everyone instead of replicating it for 2bn people?