As most people know by now, the IPv4 address space is about to run out, and this (and other problems) can be solved by migrating to IP6.
Now I keep reading in the tech press that the migration is a gigantic effort, that problems for (some) users are unavoidable, and that countless tests are required before a migration can even be considered. E.g. Yahoo IPv6 upgrade could shut out 1 million Internet users ; IPv6 move could cause network problems, threaten cybersecurity.
I don't quite understand where these problems come from. All modern OS have built-in IPv6 support, as do almost all modern mobile devices and the infrastructure (backbone routers etc.). So what is the problem that is holding the transition back?