This looks like excellent advice! I'm just in the process of automating my set up into a set of canonical ansible playbooks, and this is just another reason to do so.

Perhaps this will be even easier with the rise of docker: You ship your customer a VM that's also a docker host, you have a private index where you push new versions of your app containers , and the customers pull the new versions. Would this be workable do you think?

I haven't really looked into docker yet. So I can't guarantee anything, but it should be feasible yes.