I don't really play supers very much, so this is more my general feeling from having shared with people over various captive or coerced kinks. (A couple of them, yes snuff included.) There are definitely some, perhaps relatively few, people with a very busy fantasy snuff kink. I don't imagine that all of them necessarily must care for superheroes, but some certainly do. There are probably a smaller set of them that are set on being misogynistic themselves and a pretty small few that would happily go killing... But I don't see any reason to fuss about it more than other "hard" kinks like rape or broadly noncon pain. They can simply be their own kinks, too. I could go on about how many different kinks mainstream superhero shows play up briefly for different audiences, at different levels. But I shall umm, restrain myself. ^^
What I would guess is that the superhero genre, like sci-fi or fantasy more broadly, offers big bold powers or settings with big ranges of power and stark contrasts in some way... And you get a gathering of snuff lovers who are particularly excited to find someone to share with, all gathering around that. Does that amount to a "major kink"? I'm actually not so sure, but it's a vague term.
Personally, I usually like to keep my characters going. I'm not entirely immune to being swayed into playing a more dramatic "snap", although I'm more likely to consider death when it's rather clean and not actually permanent. I've always found multiple or competing lives and lifestyles fun, if a little dizzying to sort out with partners. On the other hand, endings are not my favorite thing to think about in general. I like ongoing tension and little changes pulled in different directions. I do like tops with a "controlling" idea provided it comes with similar tastes in the atmosphere and some playfulness... But absolutely "perfect" control can be boring and quick, permanent death is usually like that for me.