How about adding a socket activation unit in addition to the service file for
ssh?
Wondering about that in the context of MicroOS. On slow ARM devices, openssh
seems to need a noticable amount of cpu to launch at boot and may not be needed
hanging around most of the time anyways. The device's purpose mostly would be
reading sensors or such, it typically won't serve user logins. So having sshd
launched on demand via socket seems to be more resource friendly there.