I agree, we have very much approached the problem from that of service administration/management rather than the "build a PaaS"approach. But, I think the "big problem" behind building a heroku style PaaS, is not getting simple scripted deployment to a container -- it is managing relationships between applications, databases, message queues, and other connected services, and I think that is where Juju could be useful to your project.

I'd also be happy to talk more about this any time.