As far as the reason why they're appearing now, I was thinking that the organization known as DEMON exists here, as does the Trismegistus Council. In late 2012 DEMON attempted a ritual designed in conjunction with the end of the Mayan calendar to grant them superhuman powers. The Council interfered and barely managed to stop the ritual, but it increased the amount of magic in the world tremendously. And, like in the Champions Universe, increased amounts of magic enabled things like comics-style mutation and super mages to become more prevalent and active. The first generation supers would be emerging just now, a little under a year after the failed ritual.
Also, the other idea is that the PC don't have to be heroes. They're men and women who've been granted a great deal of power very suddenly so they can do just about anything. Hero, villain, something else. Just with the idea that their actions will help shape the world going forth, for good or ill.