Okay, folks: I've had an epiphany. Could be nothing, but I think there's something to it.
You see, I've figured out where Sayaka's whole "power copier" deal comes form.
...We see her with it in canon.
In Rebellion, the mermaid witch she has the ability to command other witches' familiars. (part of their power sets in other words) More than that, however, she also copies Kyoko's spear.
Why this is, is that Sayaka and Nagisa come holding on to a piece of Madoka's sealed power. And interestingly either one is enough for restoration, implying that the power is not diminished via splitting, as one might expect for copies.
On it's own, that's one thing and an interesting coincidence. However, Sayaka has also repeatedly shown a degree of sympathy for witches, just as she shows in her confrontation with Homura in Rebellion. We see it a little after the Gertrude fight as she shows sympathy for someone who "had their home barged into" and we see it again at some point around her first fight against a witch: the spider among the hanging ropes.
Sayaka's Airstep also shows some interesting traits: She shows it during the series, but what's interesting is the one time we look at it closely, during the aforementioned first fight against the spider witch, we see five imagines: knight, crossed swords, windmill, mermaid, and angel. All of these relate pretty directly to Sayaka and Oktavia. Of those, the angel has strong associations of Sayaka of Rebellion, but as far as I can tell not so strong associations otherwise. It's a very small thing that's not admissible on it's own, but in combination with the above it's more suspicious.
All in all, it's not remotely conclusive, but it points to a link between PMAS and Rebellion. And I think there's enough of one enough to warrant further investigation.
