Oh, great, we'll have to fight AM's sister sometime in the future. I bet she looks like a snarky little girl that is good in hand to hand combat. And is probably a homicidal maniac alien death goddess.
But wait, where did you get anything like that? Sure, at the very least a 'girl' like that would probably fit nicely with Kal-Rath from HMRC Pantheon, but why all of a sudden, and then 'a sister'?
Most of it was joking around and making a reference to the VR little girl.
Although it would be fun if it had a male form similar to the AMs but lighter, with some angelic references. It would be like something out of a movie, perfect for an epic duel.
But from what piecewise said looks like there is something like the AM out there, something else that is a lot like her. He also mentioned quicksilver. Last time we heard about quicksilver was when Mesk was considering getting an amp and wondering if the nano-machines in him would accept it.
The Doctor mentioned Pascal quicksivler, which means he might actually have been there for the copying of whatever the AM and the others like her ("First there were nine, then there were five, now two remain.") was made of. He also mentioned project Atavistic Herald. Atavistic means reversion to something ancient or ancestral. The herald is Phobetor, what they found in the asteroid, the beginning. But the beginning came from the future, something happening because it happened, where cause and effect are the same, like a closed time loop. So if it is from the future, evolved, advanced, then by making it compatible with the past, degrading the "flesh" of the future to something closer to its past, making something that could drink the stars into something that could fit inside a man, making it compatible with the AM, it becomes atavistic.
He also said the the quicksilver acted as a stabilising agent for the space magic of the Amps, which might mean two things: EITHER it is used to keep the AM whole and functioning well and it degrading might cause a sort of "rejection" that will be bad for her, her space magic seizing to obey her or her mind being unable to retain the focus needed, causing something similar to the Grate incident perhaps. OR it is holding back the second, stabilising it, keeping it weak and imprisoned and the quicksilver degrading might mean its release.
Either way, the existence of the second implies there is a chance we will meet the second, merely by law of conservation of detail. And even if there is a chance for peaceful resolution, unless skilled and/or lucky people are involved, it's probably going to turn into a fight (or something weird and extremely dangerous if we're lucky). Therefore, we'll probably have to fight something like the AM that is a lot like her and probably created in a similar way. Her "sister" or "brother" or sibling. The other part of the pair that remains of the original 9.
Unless of course, the other part of the pair is the Doctor. Perhaps the copying copied different aspects to each person, resulting in different effects. But that is unlikely as the effects are quite different, plus the second was mentioned to have a very large range and from what we know of, the Doctor is limited to his own body...-like-pocket-dimension-thing.
Still, makes you wonder what's different about the Living Sibling, what makes it special and why it is a good thing that the AM is not like it, if it is more powerful than her.
But that's just me making conspiracy theories. I'm probably 99% wrong about all of these.
EDIT: Hmmm.... piecewise also mentioned that a lot of sacrifices went into making the AM. So was that simply a reference to the amount of lives and resources it took to experiment and perfect the procedure or is Pascal quicksilver created from a form of human sacrifice? Or maybe it was related to another part of the experiment/creation process? Hmmm....
* Parisbre56 starts scribbling notes and pinning them to the wall, emitting intermittent giggles like a maniac, talking about how "the truth is out there".