I think it would be useful to expand the likeness of worksession to normal modeling.
In particular, It would be practical to group objects from attached files within the worksession…errr… session.
Of course, that grouping information would be temporary and not pushed to the attached file, but since you can already snap to and intersect with attached geometry, I feel that it is legit to group these objects as it does not alter them in their original file.
Grouping attached objects with objets from the active file should of course be permitted too.