The next dhcpcd release will have support for IPv6 Stable Private
Addresses, RFC 7217.
http://wiki.netbsd.org/projects/project/ipv6-stable-privacy-addresses/
http://tools.ietf.org/html/rfc7217
In summary, this is designed as a replacement interface identifier for
the normal hardware derived one when using SLAAC.
By storing a persistent secret key and combing this with stable
network information such as prefix, ssid (if available), hardware
address and a dad_counter we can then take an interface identifier
from a hash of the above information combined.
The most basic goal is that the host is no longer track-able across
different networks based on their global address, but the address
remains stable on each network.