Yup MS stated that xCloud will not have latency issues. If this is realistic across the globe than those that are worried about streaming lag can take that off there worried list.
Unless MS buys every WAN and mobile service providers in world, every back haul carrier in the world, replaces thousands of switches and routers, develops a new Wi-Fi standard with exceptionally minimal attenuation and interference, upgrades all last mile copper networks to fiber and builds Azure data centers to ensure no more than a 168 mile transmission distance, develops more efficient routing protocols with no bottleneck backbones....they have no say in latency beyond their data center.
Do a Trace Route to Microsoft and look at how many routers a packet traverses, how many different companies it is fed through, and how long it took for that ICMP Echo reply to come back.
Or you can check Azure latency with MS's own tools.
Select the regions you want and it shows you a continuous latency graph. My averages to the closest Azure DC (500 miles away - 1,000 round trip) fluctuated between 55 ms and 140 ms (seeing 101 ms pretty consistently right now). And I'm using my own data center's network (piped directly onto the Internet with no ISP). MS can't change that except for building a closer Azure data center.
Oh, and those numbers are again just a basic ICMP echo and reply. No input delay, no game rendering, no video coding, no display delay, etc....