However if you get hold on a single copy, you're not willing to publish it, as it will point to you as the source of the leak. You also can't get access to another copy, because the person that got that, has the same consideration.

So you need someone who has an access to two copies, or is trusted, by at least two people with copies, to remove hidden data.

This is time consuming. You can pick one frame at a known time stamp and some way into the movie. You can also pick 10 frames that are stenoed and 300 that are spoof stenoed = hidden in the deep woods, not worth the time to fiddle unless some one is driven.

But how would this steganograohic ID fair throughout the multiple encoding/transcoding that happens during scene distribution?

Hard to do if editing of scene cuts are differentiated as well.