I notice that there are a few changes going into the rootfs [1]. Are there
corresponding changes in the buildpack which would make them unable to work
properly in older levels of the rootfs (both cflinuxfs2 and lucid64)?

I guess the larger question is that are we going to have hard dependencies
from buildpack on the underlying stack levels?

[1] https://github.com/cloudfoundry/stacks/commits/master