"On whether or not we see Adam Warlock's cocoon: It's not Adam's cocoon"
Maybe, as an above commenter said, it's Magnus.
When Warlock was first introduced, he had no proper name. Maybe Gunn's being coy, and it's "Him".
There was also a female at one point, called "Her". Maybe it's "Her".
In any event, if that cocoon is used again, I would think that it must be something like one of the above 3. The only other cocoon-related Marvel thing I can think of is Jean Grey (her first return in FF & X-Men, leading into X-Factor #1, so many years ago).
As I'm writing, I'm thinking Vance Astro would be a good one. It brings a new GotG character into the mix, and Vance's intro would mirror Cap's first comic book Silver Age appearance, which would be cool.
Or it could be Don Ameche.