Perhaps he’ll be treated like a completely-different character who shares only Alex’s powers and codename? Well, he’s been clearly identified as Alex Summers in that character-specific teaser, so I suspect some familial details will have to change. Maybe Alex will end up being the older brother in these movies? Or perhaps he’ll be a cousin or an uncle? Could he even be (*GASP *) Cyclops’ father in this new continuity?
The likeliest answer is that FIRST CLASS isn’t too beholden to the timeline established in the previous movies and Havok is just filling in for Cyclops for the sake of variety. Before this discussion starts sounding any more like a paternity-themed episode of MAURY, let’s take a step back and look at Havok’s history in the comics.== TEASER ==
With the one of the oddest outfits to ever come out of the Silver Age, Havok debuted rather early on in X-history with UNCANNY #54. He was actually one of the first mutants to join the X-Men after the original five of Cyclops, Iceman, Angel, Beast and Marvel Girl. so he was pretty close to the "real" first class, anyway. He had been long separated from his older brother Scott after the two had been seemingly orphaned as boys when their parents were abducted by the Shi’ar during a private flight in Alaska. Because the two boys had to share a parachute, they had a real rough landing which left them with brain injuries that’d give them trouble controlling their awesome powers for the rest of their lives.
Scott and Alex’s powers have always had odd parallels. Where Cyclops absorbs sunlight to emit optic blasts he needs ruby quartz lenses to control, Havok absorbs cosmic rays to project spiraling plasma blasts he usually needs a high-tech harness to control. When they fight (as brothers often do,) they’re immune to eachother’s powers. That is, if Cyclops blasts Havok, nothing will happen.
If you want to get even more particular about the parallels, both of their codenames draw from Greek mythology - - a conceit that was continued by Vulcan, the third Summers boy.
Traditionally, Havok’s plasma blasts have been depicted as either yellow or blue in hue, but FIRST CLASS makes them red to draw an even stronger connection to Cyclops’ eye beams. While the color has changed, control is still enough of an issue for Havok that his teaser's devoted almost entirely to Professor X teaching him how to better handle his gift.
As mentioned, Havok’s had one of the more visually-distinct gimmicks in supehero comics, with concentric circles usually running in a lively pattern over his mostly-black jumpsuits. While movie Xavier’s mechanical harness allows him to focus his energy into a pulsing beam that emits from his chest - - as it does in the comics - - some creative license has been taken for the quality of his powers in their out-of-control state. As many have commented, it looks like he’s flinging hula hoops of light off of his body.
I don’t expect that FIRST CLASS will make any references to the rest of Havok’s career. Don’t expect allusions to his temporary leadership of the Brotherhood, his on-and-off relationship with Polaris, his time in the alternate world of MUTANT X or his current position as head of his father’s space pirates, the Starjammers. Considering how these X-Men are working with the government, there might be a sly nod to his later leadship of the second iteration of X-Factor (as that was the feds’ own mutant team.) Forgoing all of that, Havok will just simply be a wayward youth guided through the pangs of his mutation by the benevolent Charles Xavier.