I am trying to understand how the Realtime API Resource Model is \"shaped\", in order to work with \'get\' and \'update\' features. Unfortunately documentation
You can't use the "try it" helper to play with this feature, unfortunately. A realtime model is associated with a particular app. When you create a doc in the realtime playground, it is owned by the realtime playground app. When you try to then "get" the response in the "try-it" feature, it uses an app specific to "try-it" which can't see the realtime model you created.
If you do a "get" with the same app that created the realtime model, you should see that "data" is a json representation of the data model.
We'll work on getting this better documented.