The cloud-init package includes systemd service units, but they will fail to work correctly since the included python scripts all assume the system is using openrc.
The first file encountered causing problems under systemd is:
yes, upstream cloud-init needs a bit of love in that area and in the network config area, we are still using the 'old' netconfig stuff.
3 Years have passed and it seems that the issue remains. I just ran into it today with app-emulation/cloud-init-20.1
shouldn't a patch that's applied based on use-flags suffice to rewrite the rc-update & co lines with systemd specifics?
I faced this issue today as well, I hadn't even thought that systemd-networkd wouldn't be supported when a systemd system usually does use it.