Well technically you're already running Arch with a Debian kernel before the reboot. You could install and start services, the guide does so for sshd. Now -- taking off my pedant hat -- clearly you wouldn't want to rely on this chimera, and rather let it settle into one shape through a reboot.
My success rate with such projects is sufficiently low that I only attempt it when I have no other option. And that's for Debian -> Debian bootstrapping. Most of the time I manage to fumble a crucial parameter and the boot fails. I wouldn't even think of doing this remotely except as a challenge.
But that's not to mean you shouldn't try it for the fun of it!
If the Debian kernel supports kexec it could be even more fun.
Is there any actual utility to scripting such a thing? I'm a strange person who enjoys distro-hopping and setting up PXE servers and such, so it seems like something I'd try.
My success rate with such projects is sufficiently low that I only attempt it when I have no other option. And that's for Debian -> Debian bootstrapping. Most of the time I manage to fumble a crucial parameter and the boot fails. I wouldn't even think of doing this remotely except as a challenge.
But that's not to mean you shouldn't try it for the fun of it!