The fatal flaw with this idea, which I haven't been able to get around, is that you now spend your life entering passwords and doing sensitive work on supremely untrusted hardware.
I saw it as something he can run wherever he wants without having to migrate configs and data. Like you are flying in a different country, go to a store, buy a computer, start an hypervisor and you are done.
I would still reinstall first that new computer with an OS of my choice, but an extension of his method could be to have that qemu image stored on a liveusb that already has qemu installed. Maybe that is what he does.
Much more practical to use syncthing
To achieve the same with syncthing you'd need an aditionnal layer for the config like: git + stow, puppet, ansible, or using a distro like nix.
+ several GB of data may be moved faster from A to B using sneakernet than internet.
From the article:
> When I switch from my work computer to my personal computer I just bring the USB stick with me; same thing next time I upgrade a computer.