The following is a status update for Rails 5.1 packaging.
Foreman core has been successfully packaged as an RPM relying on Rails 5.1 and Ruby 2.4 and has passed pipeline testing. The nightly repositories now contain a Foreman running on Rails 5.1 and updated dependencies. This is the first big step to this work being fully completed.
Work has begun to get plugins and Katello built against Rails 5.1 and iron out any issues. There is a large PR  to foreman-packaging that contains updates to all packages in the plugins repository that is being used to detect issues either in the Rails 5.1 SCL or foreman packaging itself.
There are two currently outstanding PRs to tfm-ror51 that need review .