In GNOME bug 120204, someone suggests being able to pick up all the windows of an application and move them to another workspace, and also to minimise them, close them, etc. This could be done by holding down some kind of modifier while the function is being selected; this may violate the principle of least astonishment, in case someone made all their windows disappear without meaning to, merely by holding down Shift or whatever.
On the other hand, someone (who apparently used Vietnamese localisation) suggested using dialogues, with this as a possible UI:
I think this is perhaps over-baroque. I’m not sure this feature is useful enough for the downsides of either method to be worthwhile.
Photo © Jay Gooby, cc-by.