Comment 23 for bug 1391354

I'm not involved with MAAS or image building, but I seriously doubt that we build images with -proposed enabled regularly. What you could do is one of the following:

 * Boot an existing installation with "root=/dev/sda", enable -proposed, dist-upgrade, and reboot (again with the default root=/dev/disks/by-path/*iscsi*). That's what I did with the approach from Scott with launching QEMU.

 * If you are dealing with a root fs tarball: take an existing image tarball, unpack it, sudo chroot into it, within the chroot enable -proposed, dist-upgrade it, re-pack it again

 * If you are dealing with a compressed root fs image like http://maas.ubuntu.com/images/ephemeral-v2/daily/utopic/amd64/20141110/root-image.gz: gunzip root-image.gz, "sudo mount -o loop root-image /mnt", then chroot/upgrade like above, and "sudo umount /mnt" again.