Yes, an LXC container is some config files and a directory within the whole server. If you copy this directory and config files and adjust the parameters you can use it as a template. Just tar it and untar it to the new machine's directory.
answering to myself. The lxc-archlinux template is available at https://github.com/dotcloud/lxc/blob/master/templates/lxc-archlinux.in but it does not include the migration to systemd (as of Feb 15 2013) .
there are usable rootfs part of archlinux (e.g http://www.gtlib.gatech.edu/pub/archlinux/iso/2013.02.01/arch/i686/root-image.fs.sfs for i686 there also is a 64 bit version)
I did not run an lxc guest out of it yet but I got a functional i686 chroot from inside ubuntu 12.04 x64.
1/ download and unsquash the root image, mount it somewhere.
2/ as root (sudo) cp -ar the root filesystem to your location and chroot into it
3/ edit /etc/pacman.conf and update the arch line (by default it is auto, which pulls the ar ch from uname, but ubuntu and arch do not use the same designation)
4/ mount /proc /dev/random and /dev/urandom (this is needed by pacman and pacman-key)
I could not get pacman to run without package signature properly setup
5/ pacman-key --init (here it needs a good source of entropy)
6/ pacman-key --populate archlinux
7/ optional: pacman-key --refresh-keys (needs a working internet connection)
8/ edit /etc/pacman.d/mirrorlist to activate mirrors relevant to you.
9/ pacman -Syy
ready to update or install new packages.
What's (direly) missing is the container startup. I'm not up to speed on systemd but if I understand correctly this is mostly a matter of starting dbus and systemd.
Best Answer
AFAIK, we haven't working and stable solution for this task. Bleeding of edge technology for containers live migration are OpenVZ and P.Haul (part of CRIU project): https://github.com/xemul/p.haul
As main requirement I will mention vanilla kernel from kernel.org.