As to IPv4 vs IPv6, even the Zigbee folks are bowing to the inevitable. Zigbee IP uses 6LoWPAN which is a compressed IPv6 address space. The issue is not that IPv4 will go away any time soon, the issue is that v6 will happen regardless of our ability to ignore it. We surpassed 4 Billion devices on the Internet in 2009. There are expected to be 15 billion on the Internet by 2015 and 50 billion by 2020. NAT and CIDR only go so far. Eventually, we'll all have to adapt.