One of the big twists from Venom's 2020 blockbuster event King in Black revealed the true nature of Marvel's mysterious Enigma Force - a cosmic source of power that bonds with select individuals to create new iterations of Captain Universe. The story hinged on Eddie Brock discovering what the Force actually is, but if fans had been paying attention, they could have drawn the same conclusion from Guardians of the Galaxy & X-Men: The Black Vortex, published in 2015.
The King in Black crossover was all about the symbiotes' god and creator Knull arriving on Earth after breaking out of the prison planet Klyntar. After devastating much of the Marvel Universe and its heroes, the uber-powerful Knull was eventually beaten after Eddie Brock bonded with the Enigma Force. This mysterious cosmic entity has been around Marvel canon for decades, but during the King in Black storyline, it was revealed that the Enigma Force is actually a cosmic symbiote, sharing its nature with Venom while being far, far more powerful.
Years earlier, the Guardians of the Galaxy and the X-Men teamed up in order to steal an ancient and powerful artifact called the Black Vortex. An individual could glance upon their true cosmic potential by gazing into the Vortex and then actually gain that power by submitting to the artifact. All of the Guardians and many X-Men looked into the Vortex and saw powered-up versions of themselves. For the likes of Rocket and Groot, their powered-up forms are vastly different. For Venom however, his true cosmic form felt a little familiar. He had circles and lines on his body that resembled a Captain Universe costume and even had an understated mouthpiece reminiscent of Spider-Man's design when he was combined with the Enigma Force in a classic story.
Because Venom doesn't ultimately use the Black Vortex, it's never explored that his cosmic form resembles Captain Universe, but in retrospect this makes total sense. It proposes the logic that if a symbiote and their host are elevated to a powerful cosmic level, they would become a being similar to Captain Universe. With the later reveal that the Enigma Force is indeed a cosmic symbiote, this fits perfectly with Venom's lore, and yet given Guardians of the Galaxy was itself redefining the symbiotes as naturally peaceful and heroic, it seems impossible that the later reveal of the King in Black's existence was on anyone's mind at the time.
It's borderline possible that Marvel had some nascent plans to reveal the true nature of the Enigma Force many years earlier. Venom did have a short-lived series as a space knight adventurer, so it's not that hard to believe more cosmic/symbiote connections would have been revealed had that series continued longer, even if they didn't involve Knull. Fans may never know if this is an awesome coincidence or an abandoned idea brought back for King in Black years later, but it's shocking how perfectly it works even though hardcore Venom fans missed the implications of this transformation at the time.