As an example looking at the Ubuntu 18.04 dist-upgrader tarball it is possible to upgrade from Ubuntu 16.04 or Ubuntu 17.10 to Ubuntu 18.04. It should be fairly simple to add support to upgrade previous EOL releases (e.g. 17.04) to Ubuntu 18.04 and that would be a good service to provide.
As an example looking at the Ubuntu 18.04 dist-upgrader tarball it is possible to upgrade from Ubuntu 16.04 or Ubuntu 17.10 to Ubuntu 18.04. It should be fairly simple to add support to upgrade previous EOL releases (e.g. 17.04) to Ubuntu 18.04 and that would be a good service to provide.