(Transferring ~/.docker wasn't an option as I already had a set of my own hosts on my computer, and manually editing undocumented configuration files is harder than it sounds — for some reason I forgot, I couldn't partially transfer some hosts but not the other. This is after I have spent 2 days in even deciphering what has happened, as error messages are uninformative and Docker CLI just hangs in an endless loop in such situation).
Indeed, would definitely be cool to be able to export a specific machine config to a tarball that can be imported on another machine. I don't work on machine, but anyone made a proposal for this (probably with warnings about copying ssh keys and such)?
I know this doesn't help with your current issue on docker-machine, but...
I think the issue here is docker-machine's primary intent is as a developer tool to spin up dev environments quickly and easily (zero-to-docker as we say), as such the datastore and security model is tailored to this.
We are working on production-level infrastructure management, the base-layer of which you can find here: https://github.com/docker/infrakit
In essence, it is impossible to work with an existing Docker-managed host from another computer. I often work from home, and when I wanted to manage my Docker hosts from my laptop, it turned out to be impossible and this issue was closed without resolution.
This was the day when I gave up on using native Docker.
Nothing of it is documented, of course.