current upgrading requires editing the update-manager config to set a completely different host. this is super questionable from a security POV but what's more is also not entirely representative of how the actual final upgrade will work. it'd be better if we utilized the existing "devel" series system in update-manager to allow pre-release upgrades to bionic. this could still be enabled through some config file, so long as it isn't in /etc and not from update-manager.
e.g. in /etc it is a debian recognized config and triggers debconf config handling nonesense, which is not ideal