Hee, everyone wants to know how I think they’d kiss!
Well, first of all, even though by this point in the series I think it’s canon, and obviously so, that Dean and Cas are in love with each other, it’s still a pretty huge if they’ll ever physically do anything about it on camera. And it’s not because the TPTB are homophobic jerks, because they’re not. But up to this point in the story, Dean’s relationships have always been about exploring his emotions, while Sam’s relationships are about his actions and physicality. That is, over and over again Dean is asked to confront “how does this person make me feel?” while Sam must confront ‘what does this person make me do?”
It’s a way to play off the themes of the masculine vs. feminine, of internal vs. external, which comes back to who you are vs. who you choose to be, etc. So I think it’s no accident that the greatest love of Dean’s life has no physical element to it (that we’ve seen; they may very well be shtupping each other like bunnies outside what we see); it’s just the way the writers chose to emphasize Dean’s character arc.
And it should be said that love doesn’t need physical expression to be justified, or made real, or canon in a story. You can be in love with someone and never once kiss them.
But, all that said, if Dean and Cas do kiss (or more) on screen, I don’t think it will happen in Purgatory. My best bet is there’ll be a bunch of “almosts” and “so close” moments, and maybe an emotional declaration or two, but they wouldn’t actually physically seal the deal in Purgatory, at least not in flashback mode, because that would be kind of crappy writing. If it does happen, then it needs to be when it’s the most inconvenient for the characters, and when they’ll actually have to stew around in the consequences of that decision and be forced to make new decisions because of it. Storytelling 101. Which means the best time to do it would beafterthey’re reunited post-Purgatory.
If it were me? I’d probably make it happen as most first kisses usually do – not as the prelude to sex, or after some grand gesture of love, or even after a particularly great and portentous event; but in some otherwise unremarkable moment, over a beer somewhere or maybe while poring over books, a moment only made remarkable by the fact that these two idiots have finally realized the space between them is too much to handle.
But make no mistake: if and when it does happen, finally, it’ll feel no less than an apocalypse. Good first kisses always do. :)