RNG Module wait-list feature I just took a first look on the RNG Module. In the Readme, it is called the successor of the Drupal Entity Registration Module.

Is there a wait-list functionality planned or already implemented?
Maybe I'm not getting it right and its already implemented via Rules?

Any help would be welcome...
There is no support for wait lists at this time, however the API has a tagging system not exposed via UI, which is designed to support a list systems.

I encourage you to take a look at RNG Ecosystem, and give some feedback on your requirements for wait lists.