Up until the end of Changing Channels, he was the Trickster, Loki, god of mischief. Angel-seeming wasn't retroactive for me, I wasn't even sure I bought the reveal. He didn't appear having re-assumed his angelic mantle until Hammer of the Gods. He's always been the Trickster, and was that until Hammer of the Gods, where the only sexual interaction he had was with another god.
I look at Uriel, at Anna post-grace, at Michael in both vessels, even at Lucifer in The End, and none of them have an iota of humanity, let alone sex about them. Castiel is the same, whether riding Claire or Jimmy. They're just too alien a being. Sex with a human--with any being--is unthinkable. Castiel was becoming more humanized, and the squick had completely disappeared in The End. But there was no angel left--he was by then almost completely human. Zachariah is repulsive, but even when he was attempting to gross Sam and Dean out by coming on to his version of Mary, he wasn't remotely sexual, it was a perversion of the human perception of sex.
Misha is completely adorable, and Castiel is an intriguing and compelling character. I get that people want to get pretty boys together, and most of the time I'm all there. But for me personally, I just don't see the slash potential with angels. I realize I'm probably a minority of one.