Could a Future Villain Be a Former Astromancer?
I rewatched the episode "The Prophecy Unleashed", and I noticed that Nova Terron told Tazma that she wasn't the first Astromancer to turn evil. While this would later apply to Proxima, she wasn't evil at the time, so she couldn't be the Astromancer Nova Terron was talking about.
It is possible that one of the Astromancers turned evil, but then returned to the Astromancers. Nova Terron asked Tazma to come back to the Astromancers, claiming that it was not too late to do so. Perhaps he experienced this with another Astromancer, and it worked out well. This means that either one of the known Astromancers or an unknown one.
Another possibility is that the Astromancer is still evil, and Nova Terron hinting at an evil astromancer would have foreshadowed a future villain. I actually like this idea, because now that there's a new Star Mistress, it may be the perfect time to make the Astromancers more relevant to the plot. The new villain could cause problems for Proxima, who may struggle adjusting to her new position and/or getting the other Astromancers to trust her again. This would also work well for Tazma, as working with a person who turned away from the Astromancers may cause her to reflect on her actions. If the Former Astromancer is still evil, I doubt that it would be someone we know, as every possible former Astromancer was given a reason for leaving (though Alpha Galaga's demise could be faked, they speak too fondly of him for me to suspect him as being evil).
In short, that one line of dialogue could have been explored further if the series continued, either by one Astromancer revealing their former evil past or a former Astromancer being a future villain. I personally like the idea of the former Astromancer being a villain.
