Comment 1 for bug 1574076

The Suggests is dual purpose for Xenial. Both does the normal job of informing the user of the new juju 1.X specific package, but is also a tricky upgrade hack. The release team noted that the upgrade process now autoremoves packages in its default behaviour, so going to Xenial and 2.0 juju would take away everyone's working client. The Suggests on the old package name avoids that. A Suggests on the new package name would not, and 2.0 juju doesn't really want to Depends or Recommends on 1.X juju.

For Y, the old aliases and other transitional elements related to package upgrades from 1.X should be removed.