Currently you can only draw straight Split Lines in the Sub Modify Elements. It would be better if you could draw Split Lines like you draw lines in other edit modes in Revit. This would enable us to draw rectangles, use pick lines and other tools.
Another important feature that could be enabled is curved Split Lines. The Boundary Lines of a Toposolid/Floor/Roof can already be curved, so it should be possible to have curved Split Lines too.
Ellipses should be possible but isn't a priority. I get that Splines won't be possible.
