I’m a bit hesitant to describe something that seems obvious after stating it, but:
I see no reason why it wouldn’t possible to boot devices from an OS image kept on the SAFE network. When powered on, a device’s built-in operating system (BIOS) does some health checks and then looks in mass storage, or in some cases on the local network, for the operating system, and then loads it. But that network could be the SAFE network.
For IoT devices, the boot image might include an initial database for it to do its job and to find sibling devices.
For bigger systems, such as general purpose computers (which, of course, can be as small as a Raspberry Pi), it depends on how long you want to wait for it to boot. I imagine though that in a situation where you have a population of such devices, such a boot image might be downloaded once and then cached locally perhaps on the first peer to boot…