Honestly, I think a significant part of why I like that coded liminal space so much is because (as we established on this journal previously) I hate all canon ships, so I want ships that are safe from ever being ruined by canon :P But yes! Poly coding is definitely something I'm seeing in mainstream media these days (and has been around since those Hays code movies too, cf Singin' In The Rain.) It's interesting the way it interacts with the portrayal of deniable queerness, too - if you have well-developed canon het right there, it seems like it's a lot easier to get away with old-fashioned queercoding. You don't have to have Eliot and Alec loudly deny any possible gayness, because you can just point to Parker in the middle and get away with letting the homophobes pretend canon m/f means they can't possibly be into each other while making it perfectly clear that they are.

It actually reminds me a lot of the 'conduitfic' meta I was seeing in slash fandom fifteen/twenty years ago, talking about how slashers would use a female character as a 'conduit' to let the male characters have sexual interaction without directly confronting homosexuality - I feel like we're seeing that more and more in queercoded canons now, as slash has mostly stopped bothering.

...of course that does in large part rely on bi invisibility in mainstream media to get away with it, sigh.