First thought was Kree( or Doctor Manhattan). Still think Skye is a pink Kree.
+1 on the Kree theory, including Skye.
But a little early for a DC crossover, don't you think?
I'm thinking Kree, too, and wouldn't be surprised if Skye was some sort of Kree hybrid like Carol Danvers.
Even though this isn't a surprise to anyone following, here's a non-show spoiler (if it was for the show, I wouldn't use the tags) for an upcoming movie, in case someone is avoiding the information. . .
As for The Clairvoyant, I'm only aware of a few precogs in Marvel (Destiny, Blindfold, a few others). Could it be a time traveler?