Rooted elements, in my opinion, should represent highly identifiable, first-class domain-specific objects. I believe
IfcMaterial fits this criteria. In addition, materials are usually represented as their own user manipulatable, export/importable, object in most authoring applications - not just a mere property, but an object in its own right.
Materials also have significance in LCA analysis, modern slavery tracking, warranty and certification for facility management.
I am also painfully aware of the current poor vendor support for IfcMaterial, leading to confusion between material and colours, which are related, but separate concepts. Hopefully, with an upgrade of IfcMaterial to a rooted entity, it will also gain more widespread and proper usage instead of being lost on imports and exports.
Therefore, I propose for IfcMaterial to become rooted, and therefore have a GlobalId associated with it.