I have made debian packages for 4.2.0, to be found at
http://primate.net/~itz/debian/polyml
Tested only on i386.
I added a bit of infrastructure to maintain the chain of child databases for libraries. I myself intend to package a couple of libraries from the net, such as FGL and FXP. Later I'll tackle either Isabelle or ProofPower, but that will be a much bigger job.