Ketch and Mary
I just have one shallow comment....
I want to see Mary and Ketch hook up (again) and get together as a couple. First, I think they make a good looking couple. Second, I think he sees her as one of the few women who are his equal when it comes to hunting monsters.
I can think of a scary-dangerous, but funny, situation where Mary and Ketch get pregnant. While there is the danger of a pregnant hunter (scary-dangerous) there is also the (funny) prospect of Sam and Dean not only wrapping their minds around the idea that not only are they going to have a little (half) brother or sister, but that the father is someone they have had a love-hate relationship. In fact, I can see Jack being the only one who consistently thrilled about the pregnancy and having a new baby around.
Mary is a bit older than Ketch but not by that much, maybe later 30s, early 40s. In theory, she could still get pregnant.
Of course, if they ever kill Negan off on The Walking Dead, maybe they can find some hocus pocus way of bringing John back. I could see he and Marry having some crazy firework chemistry and it would be pretty funny to see Sam and Dean (who by this time are what, in their late 330s) have a newborn brother or sister.
OK, I think too much about this.
But when is Ketch coming back? The boys are cute, but he's how and I bet a real dirty boy in the bedroom. And yes, I probably need a cold shower and some saltpeter :D