When applying a Normalize Spline modifier on a shape the Material ID for all segments are reset to 1.
It is understandable that it is hard to preserve individual Material IDs on a connected spline. However, if you just want all of the spline to be the same Material ID there should be no problem for the Normalize Spline modifier to set all segments to that Material ID value.
There is no currently no simple way to set Material IDs for segments while preserving Spline functionality. Applying the Material modifier converts the spline to an Editable Mesh, which is not desired. Applying an Edit Spline modifier on top in the Stack requires manual rebuilding whenever the amount of segments is changed in the Normalize Spline modifier.
We either need a Set Material ID feature inside the Normalize Spline modifier, or a standalone modifier that can set Material ID for splines without converting it to any other type of object (preserving Spline functionality).
