Hi Eric - for now, it looks like you can manually move everything to the top level layer and grouping stays intact - I realize it is not the whole job but you can, perhaps relatively painlessly, get it done
_Make2d Pause Pause Pause -ChangeLayer "LayerName"
There is still some management dealing with the emptied layers - you can include a Purge in the macro but that might be too heavy handed:
_Make2d Pause Pause Pause -ChangeLayer "LayerName" Purge BlockDefinitions=No AnnotationStyles=No Groups=No HatchPatterns=No Layers=Yes Linetypes=No Materials=No Enter
-Pascal