This theory was initially composed by Gabe Brady and expanded upon with evidence from the Marvel comics and other fine-point details by yours truly.
A plotline that has been dragged on for a bit too long in Marvel's Agents of S.H.I.E.L.D. is the true nature of Skye, played by Chloe Bennet, and her terrifylingly psychotic father, played by legendary Twin Peaks/Blue Velvet star Kyle MacLachlan. As of right now, we know only a few details of Skye's backstory: she's an 0-8-4 (object of unknown origin, pretty much confirmed alien by Coulson in the latest episode), is most likely somehow related to the Kree species, and has an evil father who is a "monster".
Her father himself has shown signs of superhuman strength, terrible anger problems, a heavy interest in alien weaponry, vague connections with the HYDRA organization, and a terribly awkward and forced manner of speech. Having seen Kyle MacLachlan play many characters before, his voice has always been smooth, and it almost seems as if Kyle's lower jaw is stretched to the point of intentionally trying to alter his voice, in-character. This could be written off as being because Kyle is trying to come off as gruff for his character, but I actually think Skye's father is forcing a gruff American accent upon himself to hide his German accent and protect his true identity as the Red Skull.
Additionally, Drew Pearce once teased a Sin one-shot movie, meaning Marvel has room for Sin somewhere in their master plan.
What does this mean about the tub of blood Skye's father was sitting in at the end of season one? Perhaps this is the Red Skull's method of growing new skin to assume the identity of Kyle MacLachlan. No way they'd be bringing back Hugo Weaving after he openly badmouthed Marvel. Anyway, thoughts?