I’ll add some update information around the packaging effort that is required as well. This is strictly RPM based since Debian uses gems more directly and thus does not require building an SCL.
The previously named tfm-ror51-packaging repository has been renamed to rails-packaging and the default branch set to tfm-ror52. The set of packages available currently matches all previously required packages. A test repository of just the Rails 5.2 SCL can be found here.
The current status is that of test building all of Foreman packages against this new SCL and making updates to existing packaging where possible ahead of time. Thus far the amount of required changes has been minimal. The packaging effort should align well with the target dates.
Also note that with this upgrade to Rails 5.2 comes an update to Ruby 2.5 for RPM based deployments.