@londonfog I’ve also gotten autoinstall to work with the following imgargs
imgargs vmlinuz initrd=initrd root=/dev/ram0 ramdisk_size=1800000 ip=dhcp url=http://172.16.13.3/ubuntu-20.04.1-live-server-amd64.iso net.ifnames=0 autoinstall ds=nocloud-net;s=http://172.16.13.3/2004/ ro
boot
172.16.13.3 is my fog servers ip address, emphasis on this string
autoinstall ds=nocloud-net;s=http://172.16.13.3/2004/
That part of the sting tells subiquity were to find the user-data and the meta-data files. http://172.16.13.3/2004/user-data has the yaml containing all the autoinstall parameters, http://172.16.13.3/2004/meta-data is just a blank file. Both files need to exist in order for subiquity to perform an autoinstall. subiquity is also extremely strict about the formatting of the yaml within the user-data file. I found this out when attempting to copy/paste another user-data example from the internet only to crash the live installer. I had to hand write all the parameters in user-data in order for it all to work. this is what my user-data file looks like.
#cloud-config
autoinstall:
  interactive-sections:
    - storage
  apt:
    geoip: true
    preserve_sources_list: false
    primary:
    - arches: [amd64, i386]
      uri: http://us.archive.ubuntu.com/ubuntu
    - arches: [default]
      uri: http://ports.ubuntu.com/ubuntu-ports
  identity: {hostname: 69changeme69, password:  PASSWORD HASH,
    realname: companyadmin, username: companyadmin}
  keyboard: {layout: us, toggle: null, variant: ''}
  locale: C
  network:
    ethernets:
      eth0: {dhcp4: true, dhcp-identifier: mac}
    version: 2
  ssh:
    allow-pw: true
    authorized-keys: []
    install-server: true
  packages:
    - ubuntu-desktop
    - landscape-client
    - openjdk-8-jdk
    - libpwquality-tools
    - wpasupplicant
    - python
    - python-dbus
    - python-argparse
  late-commands:
    - | cat <<EOT >> /target/lib/systemd/system/postinstall.service
      [Unit]
      Wants=network-online.target
      [Service]
      Type=oneshot
      ExecStart=/opt/postinstall.sh
      RemainAfterExit=true
      [Install]
      WantedBy=multi-user.target
      EOT
    - systemctl daemon-reload
    - wget http://172.16.13.3/2004/postinstall.sh -P /target/opt/
    - chmod +x /target/opt/postinstall.sh
    - echo 'companyadmin ALL=(ALL) NOPASSWD:ALL' > /target/etc/sudoers.d/companyadmin
  version: 1
This installs mostly automatic. I have mine set to prompt for partitioning. Hope this helps