Are there any unexpected Spatial problems going from 11g to 12c?

We are starting to think about upgrading from 11.2.0.3 to 12c, and as a heavy user of Spatial functionality, we are worried about what unpleasant Spatial surprises this might involve.

Upgrading from 10g til 11g a few years ago was difficult, as I had not been aware of that 3D arcs were no longer supported. Compound line strings are thus also not supported, since they exist in order to combine arcs and line strings.

sdo_geom.validate_geometry_with_context returns errors for them, but otherwise they seem to work. Only really degenerate cases - like a compound line string consisting of only one line string -  prevented creating a spatial index (which it didn't in 10g). Of course, there is no reason for a single line string to be of compound type, but in the real world such elements do exist, and finding and correcting them can be time consuming.