So I would propose to integrate LXC/LXD updates to the latest released versions and put them in a new prime branch?

Here are the latest versions:

• LXC
  • 1.0.11 (Please note that LXC upstream strongly recommends 1.0 users to upgrade to the 2.0 LTS release.
    The 1.0 branch will keep being supported until June 2019, but at this point,
    only critical bugfixes and security updates will be backported.)
  • 2.0.9 (LTS 2.0 series is supported for bugfix and security updates up until June 2021)
  • 2.1.1 ("latest stable branch")
• LXD
  • 2.0.11 (LTS - EOL June 2021)
  • 2.21 (stable)
• LXCFS
  • 2.0.8 (LTS - EOL June 2021)