These are mostly what the current OpenStack image supports (apart from Hybrid), and which we probably want to see within the published images.

* cloud-init with this list of metadata sources in /etc/cloud/cloud.cfg.d/90_dpkg.cfg:
  - datasource_list: [ NoCloud, ConfigDrive, OpenNebula, Azure, AltCloud, OVF, MAAS, GCE, OpenStack, CloudSigma, SmartOS, Ec2, CloudStack, None ]
* Support amd64 + arm64
* Must resize itself (partition + resize of the fs)
*  password or ssh key defined, cloud-init does it
* tty + ttyS0 for:
  - grub (please fill...)
  - systemd .service unit printing (aka: systemd.show_status=true)
  - getty consoles as per http://0pointer.de/blog/projects/serial-console.html
* Latest kernel installed, a single cloud kernel.
* No unattended-upgrades
* Single kernel installed after securty updates
* Set console for emergency and rescue shells (ie: emergency.service rescue.service)

Nice to have:
* Hybrid BIOS + EFI (grub-cloud does that...)