WMG: The Reckoners Trilogy

Megan will begin using her powers to cure epics, and inoculating people against calamities power
Since we now know that epics can be cured of Calamity's corruption by facing their worst fears, and that ordinary humans can be made immune to epic transformation through the same method, a powerful illusionist is exactly what they need now. I can even see it becoming a cultural tradition in the long term if Calamity isn't destroyed, a right of passage where everyone has to face a simulation their worst fear.

Calamity and the Epic Powers are based on the power of fear
It certainly works symbolically. Fear grants people extraordinary strength and the ability to do the otherwise impossible, but also makes people selfish and violent. But, if you overcome the selfishness through bravery, it can let you accomplish great things and can bring out the best in people. This is pretty much exactly how epic powers work, given the revelations in Firefight. It's possible that this is literally true as well, with Calamity being some sort of embodiment of the transformative power of fear.

No one really makes technology based off Epic powers

There's an obvious hurdle in emulating their powers, which is that they're explicitly physically impossible. Steelheart's most advanced equipment and the Reckoners' gear is based off Transference Epics. The arms dealer who provides highly advanced equipment takes payment in the preserved, still-living cells of Epics. This is supposedly for research purposes, but quite possibly has the real purpose of installing cloned cells into the technology, actually using their powers directly instead of merely imitating them. The gun he sells to the Reckoners may actually be an exception; it's a coilgun (so we know how to make it today, in theory) that shoots highly energized projectiles and has a higher power draw than Newcago. If that were representative of the difficulty of replicating Epic powers scientifically, it would not be a thriving research field.

Prof killed his fifth grade class by accident after the Calamity
That may be why he hates using his power so much. Using powers makes people more evil, and the manifestation of his powers might have made him lose control.

Prof made the Diggers
It's mentioned that the Diggers were gifted powers similar to the Tensor devices to dig underground. In the end, the Tensors are revealed to be Magic Feather s and Prof is really a Gifter Epic. Why he would do such a thing remains unclear.

Prof is afraid of the 'pattern' in Epic weaknesses because it means someone might find his
. For someone that makes his life killing Epics, he's awfully insistent that there is no pattern. And he himself is an Epic, after all.

All Epics are psychopaths because Calamity is a psychopath
. With The Reveal in Firefight that Calamity is itself an Epic, and that all other Epics receive a shred of his power, it's at least possible that the madness that comes with the powers is a reflection of Calamity's own mind.

Calamity really is an Angel
, and the Epics are the true "Reckoners" the series is named for As Obliteration mentioned in his monologue towards David, he considers that the Four Horseman actually are not "individuals" but metaphorical. One could easily pass it off as the ravings of a psychopath (given Obliteration's track record), but Regalia not only called Calamity an Epic, but described Calamity as the Destroying Angel. In other words, since Calamity is the one who creates the Epics, it and the Epics are collectively the "Reckoners" of Humanity with the coming of the Apocalypse.

Obliteration will undergo a Heel-Face Turn
At the end of [1], Obliteration thanks David for giving him the answer to his nightmares and disappears from the book. We also know that Megan no longer suffers madness from using the power of an Epic, so it is entirely possible Obliteration went off to conquer his fear and regain his Humanity. meaning he will likely show up in Calamity.

Calamity is the same type of being as Scion from Worm.
In Worm, Scion is a glowing, divine-looking, power-granting alien. Calamity comes from the same place, but is employing a different strategy with his power investment.

Tia will be the key to stopping Prof
. We know that the key to overcoming the corruption is the Epic's greatest fear, something from their past. So surely a person who actually knew the person before they became an Epic would hold the key. Failing that, it's also possible that Tia already knew Prof's weakness as a failsafe in case Heroic Willpower finally failed. Seems likely that reaching her before she can be killed will be a priority in Calamity.

Prof is afraid of taking risks.
Before Calamity, he was upset because somebody won a prize in a contest he didn't even enter, and his ex-girlfriend Tia says he never gambled. According to the pattern seen with other Epics, this means Prof's powers fail him when he indulges in games of chance, or otherwise takes risks. This explains why the Reckoners are slow and methodical. It's because Prof is risk-averse. His actions at the climaxes of both books don't count, Steelheart because he was never in any personal danger from Steelheart, and Firefight because, ironically, David convinced him it was a sure thing.
  • This makes a great deal of sense. And that's also why he attacked David IMMEDIATELY on rising as a High Epic, because letting the person most likely to be able to kill him live is also an unacceptable risk.

Calamity didn't fail in making David an Epic.
David might still have powers thanks to his contact with Calamity, he just hasn't used them. He might not even know he has them, and they'll manifest at an appropriately dramatic moment.

Alternative Title(s):

Steelheart, Firefight