We have a series of locations that determine replication topology, but you cannot do à la carte region selection at this time. Under the hood we run on at least 3 independent private super fast network fabrics between regions, so we have a pretty high bar infrastructure wise for deployments. We bet on having reliable high-grade deployments and Google's world wide network to get requests to users faster rather than stretching out arbitrary deployments. Seems to work so far for customers like Snap & Niantic Labs (Pokemon GO), but YMMV.