Spoilery theory about Guardians of the Galaxy 2
1. James Gunn has confirmed that the cocoon seen in the Collector's museum is that of Adam Warlock. So, Adam Warlock is confirmed to exist in the Marvel Cinematic Universe.
2. Peter Quill's non-human heritage is given as the reason why he was able to bear an Infinity Stone for so long. This may well be deceptively important, because...
3. Adam Warlock is the full-time bearer of another of the Infinity Stones, the Soul Gem.
4. Peter Quill's mother described her son's non-human father as 'an angel, a being of pure light' which is a pretty good description of Adam Warlock if you're an emotional Terran.
5. Yondu described the same guy as 'a dick' which is also a pretty good description of Adam Warlock if you're a gnarly space rogue.
6. James Gunn has suggested that 'at least one other' of the comic-book Guardians should turn up in the movies.
7. Conclusion: Adam Warlock is Peter Quill's father in the MCU.