I suppose it depends on what the purpose of saved selections are used for.
If it is for textures and shaders and possible morphs, then shading domains work just fine.
If you need a hierarchy for animation then extract the polygons and make it part of a group hierarchy in a parent/child relationship.
Just because you use shading domains, doesn’t mean they can’t be useful. One can use shading domains across several regions of polygons if they have the same texture. Also, shading domains don’t have to be different colors or texture, they can be used to identify function.
For instance, gear shift linkage can be the same color, but each one can be given a shading domain so it can later be used to animate separately as “parts” in most 3D graphic programs.