We have found that Warden's features are hard to implement on top of libcontainer, mainly because of the way libcontainer manages user processes. So we have decided to defer development with libcontainer until such time as the implementation stabilises (i.e. after libct is integrated) at which point it may be worth having another look.
We are, however, planning to reuse some of libcontainer's Go packages, specifically netlink, which match our requirements.
(Please note that Garden, the Go variant of Warden, already supports using Docker images as container root file systems.)