Support for automated publishing of registered layers from aprx?

[ShaneBuscher]

When manually publishing a web layer in ArcGIS Pro there is an option to specify registered data as the source instead of using the ArcGIS Data Store in a hosted scenario. The desire is to automate this exact manual process. However, I'm finding all APIs falling short because they only support hosted layers. In particular, 

1. ArcPy 3x:  CreateWebLayerSDDraft 
2. ArcGIS API for Python: arcgis.gis.Item.publish() 
3. Portal REST API: <url>/publish

All three do not support non-hosted layers, such as registered data. Still looking into arcgis.ContentManager.create_service()- it doesn't explicitly say one way or another whether this supports registered data. 

Do any APIs, or combination of them, support publishing web layers with underlying registered data from an aprx? I can't image why this wouldn't be exposed (?). 

[ShaneBuscher · Accepted solution]

Found out from Dev Summit that this is currently not supported but is being worked on by ESRI with a possible beta release June 2018.