>3. History has shown that upgrading network backbone hardware (in particular) is incredibly difficult through a process that's been described as "ossification"

>3. History has shown that upgrading network backbone hardware (in particular) is incredibly difficult through a process that's been described as "ossification", which is a nice description. Basically, network relays and routers wanted to avoid security issues and decided to discard things they didn't understand. Would say the opposite is true. Core routers were the first to enable V6 support in any network as they would need support it for anything else to even use it. They got regularly replaced as bandwidth needs keeps rising as well. Plenty of isps advertise ipv6 but haven't managed to give it to customers yet. Interrupts are hardly a problem with any nics of the last decade really. Companies like Facebook can and do use 240/4.