Landlock currently isn’t in mainline; it’s only in linux-next: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/Documentation/userspace-api/landlock.rst?h=next-20210319&id=f00397ee41c79b6155b9b44abd0055b2c0621349
When it does land in mainline, it will be a very long time before it reaches LTS and besides, I don’t see a significant advantage of this over AppArmor + bubblewrap. Landlock is intended for use cases in which the user does not have the adminstrator privileges necessary to configure traditional security policies like AppArmor which does not apply to us.
Combining a whole bunch of different access control mechanisms would be redundant — it’s the same kernel enforcing all of these policies and a single kernel exploit can bypass all of them. Unless Landlock exposes the ability to restrict something that isn’t already covered by our current approach, I don’t see an advantage.