We are still using it for some one off use cases to limit what classes show for a given service variant and would prefer to keep it available, but I haven't looked closely enough at this PR to see if this would work in replacing that use case with something better.  We really just want to have a URL or service variant that shows a subset of classes (definable in settings or by course org).  We don't currently use sub theming for that use case, but it could be nice.