Four days ago, The FBI warned ISPs not to use IPv6. IPv6 has been used by AT&T (U-Verse), Verizon (FiOS) and other cable companies.
IPv6 makes it hard for law enforcements and the federal government to track every internet user and easier to keep users data private. But there's IPv5, which make privacy obsolete.
IPv4 was known spreading malware like the Mytob worm.
IPv6 requires users to change their equipment, from DSL to cable internet. AT&T DSL to U-verse, Verizon to FiOS, already occurred, even ditch their older OS systems and use Windows 7 and higher.