Warning: SPOILERS for Guardians of the Galaxy Vol. 2 are ahead!
One of The Collector's prized possessions in his museum before it was destroyed was a mysterious yellow cocoon, seen in both Thor: The Dark World and Guardians of the Galaxy. When Marvel fans spotted this, there was immediate speculation that this cocoon contained Adam Warlock, as he emerged from such a chrysalis in the comics. That turned out not to be the case, and Warlock was later set up in one of Guardians of the Galaxy Vol. 2's mid-credits scenes. However, director James Gunn has revealed that the first cocoon, like the one Warlock will eventually hatch out of, is also connected to the Sovereign race. As he put it:
With Guardians of the Galaxy Vol. 2 having been out for almost two months, James Gunn provided the above response when asked on Twitter if the cocoon seen in the first Guardians of the Galaxy movie contained Jean Grey's body when the Phoenix took over. Given how 20th Century Fox has the film rights to the X-Men characters, it's extremely unlikely that Gunn would have ever been able to include such an Easter egg in his MCU feature. The Sovereign explanation fits much better within the MCU continuity following Guardians of the Galaxy Vol. 2's release. Since Ayesha, the Sovereign's High Priestess, called Adam a new member of their species, it makes sense that their ancestors could have come out of cocoons like the one The Collector acquired. As time passed, they found a way to enhance the cocoons, eventually leading to the one that Adam Warlock will one day come out of.
Since The Collector's museum was destroyed in Guardians of the Galaxy when his slave, Carina, grabbed ahold of the Orb (a.k.a. the Power Stone), it's unlikely that particular cocoon survived the explosion. It fulfilled its purpose as an Easter egg, and that's that. Adam Warlock's cocoon, on the other hand, will be back at some point. After the Sovereign were defeated yet again in Guardians of the Galaxy Vol. 2, an exhausted Ayesha told one of her minions that she would create Warlock as the weapon to destroy the Guardians once and for all. While some Marvel fans long suspected that Warlock might show up in Avengers: Infinity War given the role he played in the Infinity Gauntlet storyline, it's been confirmed he will not show up in that epic event, and instead will be saved for a different Marvel movie.
Guardians of the Galaxy Vol. 3 is scheduled for release in the coming years, and that's likely (but not confirmed) when we'll see Adam Warlock awaken. But before that, the Guardians will return for Avengers: Infinity War on May 4, 2018.
