This has come a long way without any update as there was little attention to it by an audience, but the plugin has been released for early adopters and we’ve entered a stabilization period, that will most likely take two releases.
If you can, please help testing it (install tfm-rubygem-foreman_puppet / foreman-puppet with your 2.4 version update) 
For more details I’ve made a separate post [1].
What’s left:
- Finalize some extraction [2] to be ready for the final removal from core
- Add the plugin to installer
- Documentation needs to be extracted
- SmartProxy plugin needs to be created
[1] Puppet plugin release annoncement Puppet plugin release and its future
[2] List of extraction PRs Pull requests · ezr-ondrej/foreman · GitHub