I would want to object and say "There is IPv6 in the cloud!".

We have developed re6stnet in 2012. You can use it to create an ipv6 network on top of an existing ipv4 network. It's open source and we are using it ourselves internally and in client implementations since then.

I wrote a quick blogpost on it: http://www.nexedi.com/blog/blog-re6stnet.ipv6.since.2012

The repo is here in case anyone is interested: http://git.erp5.org/gitweb/re6stnet.git/tree/refs/heads/mast...