I think the biggest problem with superheroes (though I WANT THEM SO BAD) is that they have to fit into the domestic setting of The Sims.
The more outlandish powers, eg. Thor-style lightning powers, are gonna end up being essentially souped-up Mischief interactions, just like the magic Spellcasters get, and tbh those are kind of lame. Magneto-style magnetism might be like an Alien's repair power, and a Kitty Pryde "phasing" power could be a Ghost's possession power. Which are... not that exciting.
Super-speed is doable (Vampires have it already) as is super-strength and teleportation (again, Vampires), but I can't see anything else really working.
At the end of the day, what will superpowers really bring to the table?
