Hi @jason,
not sure if this is as straight forward compared to the macros.
We know from Unable to detect page copy event when copying page without children that two events are fired. But I doubt that you can get the source page from that.
ContentEntityProperties are not copied, according to @BobBergman, thus there is no easy way to store the current page-id in the entity properties and use that for comparison.
No other ideas right now. Let me think about it some more.