Warning: contains spoilers for Heroes Return #1!
Marvel takes Superman's weakness to its logical conclusion.
Heroes Return #1 marks the beginning of the end of the Heroes Reborn event, in which President Phil Coulson collaborates with Mephisto to reshape the world as he sees fit. In Coulson's ideal universe, the Avengers never gathered together, and so the greatest superhero team is the Squadron Supreme: a group of seven superheroes that closely resemble DC's Justice League. The mysterious and brooding Nighthawk is the analogue to Batman, space-traveling Doctor Spectrum is Green Lantern's analogue, and the stand-in for Superman is an ultra-powerful named Hyperion. Though Hyperion is far more aggressive than Superman, he remains Earth's strongest hero and a symbol of hope to the masses. His strength is tested, however, when he comes across his greatest weakness.
In the climax of Heroes Return #1, the re-assembled Avengers clash with the Squadron Supreme in Wakanda (which, unlike Marvel's main universe, has remained closed from the rest of the world), and Hyperion picks a fight with Thor. The fight with the God of Thunder exhausts him like no other in his life, and he begins to feel quite weak - he's even broken his hands. Nighthawk has deduced the reason why. "Vibranium. The meteorite that brought it to Earth was a chunk of your homeworld. Its radiation will likely kill you." Nighthawk and Hyperion steel themselves for their final fight against these strange "Avengers," but the implication of the former's deduction isn't lost on fans of DC's Superman.
In the Heroes Reborn universe, Hyperion is as weak to Vibranium as Superman is to Kryptonite. It logically follows that if a large enough meteorite of Kryptonite fell on a landmass in the DC universe, an entire country would be impossible for Superman to enter - at least, not without greatly weakening him. The entirety of Wakanda is literally poison to Hyperion, and could even kill him if he stayed long enough. Against a country full of Kryptonite, Superman would have a similar problem.
Marvel has heavily used this technique throughout Heroes Reborn to strongly criticize the Justice League without actually including the Justice League in their books. At the conclusion of Heroes Return #1, the universe is restored but the Squadron Supreme remains, lost without purpose or any allies. If, for all intents and purposes, Hyperion is Superman, then he shouldn't have any trouble finding new friends and forming new partnerships - so long as he doesn't stumble into Wakanda.
