IfcMaterialProfileSetUsageTapering cannot specify the second profile at the type level

For all other material sets, they can specify the profile(s) / layer(s) at the relating type. Then, all occurrences of that type will have a material set usage pointing to that material set, and the representation is expected to comply by either using the same profile as its extrusion profile or have the same total layer thickness.

Except for IfcMaterialProfileSetUsageTapering. There is no IfcMaterialProfileSetTapering equivalent, which means that the type can only be a regular IfcMaterialProfileSet which defines only one (potentially composite) profile. However the usage requires 2 profiles (start and end).

This is inconsistent with regular material sets and set usages, and implies that there is no way to predict the other profile of the occurrence. In theory, every occurrence can then point to a completely new instance of IfcMaterialProfileSet that isn't referenced anywhere else. This sounds semantically dubious (imagine a model full of profiles tapering to random other profiles all being the same type).

One proposal is to introduce a IfcMaterialProfileSetTapering equivalent.

Another proposal is to deprecate IfcMaterialProfileSetUsageTapering as a complex usecase that doesn't fit the "standard case" of simple extruded profiles.