FWIW, this is almost exactly what I needed. I was already using vm-bhyve. With a few tweaks, this does exactly what I needed for rapid spinup direct from unmodified "cloud" images:

# vm create -t linux-uefi-zvol -s 20g -m 4g -c 2 -C -k /root/.ssh/authorized_keys -n 'ip=10.0.0.111/24;gateway=10.0.0.1;nameservers=10.0.0.1' kube-11
# qemu-img convert -f qcow2 -O raw -p /vm/.iso/noble-server-cloudimg-amd64.img /dev/zvol/zroot/vm/kube-11/disk0

No installation, no dhcp, static network config, no custom images.

Tweaks: I fixed multiple ssh keys, changed ahci-cd to virtio-blk (which stops a bunch of linux kernel noise), and changed gateway4 -> routes since that generates a deprecation warning on modern clients.