I think the parent is talking about that behavior, but extended throughout the entire OS. You can see this in some apps, one that comes to mind is Sketch and its concept of "symbols".

I think the complaint is that copy/cut/paste was weak in the beginning, and generally just worked with plain text. This weakened the metaphor to where now we don't expect much else, but it could have been much more powerful.

I believe it was a per application design. File explorer could copy folder and files (windows too). But you can't copy anything out of the box.