Ok good to know, did not know that.
So I now have the code working, but still not as expected as the curves are still not associated to the plane. Currently i have been able to set the sketch plane to the work and then rewrite them out to this plane. But maybe because this plane currently is not named or referenced from a Reference line it is not linked if you click on the curves in the Revit.
The plan is to have a plane that can be rotated in Revit with a Parameter and the curves associated to this so the curves in the family change rotation independent of Dynamo.
Latest python Code including loop so it does all curves. I realise it would be good to make the output a print to say it has been completed or event the new model curves just not go that far yet.
from Autodesk.Revit.DB import *
from RevitServices.Persistence import DocumentManager
from RevitServices.Transactions import TransactionManager
doc = DocumentManager.Instance.CurrentDBDocument
# The inputs to this node will be stored as a list in the IN variables.
modelCurves = UnwrapElement(IN)
sketchPlane = UnwrapElement(IN)
doc.ActiveView.SketchPlane = sketchPlane
for modelCurve in modelCurves:
# Assign your output to the OUT variable.
OUT = 0