The most alone they’ve ever been
Series executive producer Andrew Dabb told Variety that “This will be the most alone Sam and Dean have been…They don’t have Castiel, they don’t have Crowley, they don’t have Mom, they don’t have Rowena. They have each other and this weird kid who could probably kill them if he wanted to.”
Everybody grieves differently
In terms of the effect losing Castiel has on the Winchester brothers, producer Brad Buckner said:
"This profound sense of loss lingers over several episodes. He’s not coming back real soon, and it influences, greatly, Dean’s state of mind… this overwhelming loss at the start of the season is something that Dean just can’t dig his way out of yet."
Sam and Dean become the foster parents of Lucifer’s spawn
There’s going to be some real nature vs nurture stuff going on this season as Sam and Dean work to raise Jack, the son of Satan, often coming to blows over their parenting methods.
As Jared Padalecki told Variety – “I feel like Sam believes [Jack’s] good. With all of the s–t that’s happened – all the wrong roads he’s taken – Sam still has this optimism, this hope. He’s trying to manifest that onto Jack, whereas Dean, especially in [the first episode], he’s concerned [Jack’s] not [good].”
"It's interesting,” Jensen Ackles said at 2017’s SDCC, “‘cause mum is gone and presumably dead, Crowley just killed himself, Cas is now lying dead at Dean's feet. Kelly's gone... it's too much for Dean to process at that moment.
"So he does the thing that he knows how to do best and that is neutralise the threat – as in, Lucifer's son – so he's just gonna do that, 'cause that's something that he can hit. There's too much emotion, he doesn't know how to process, so he's just gonna do what he knows and that's hit something – hard."
While Dean has given his mother up for dead, Sam is hoping Jack can open the rift again.
“Who knows if it’s a sensation or a feeling he has or dumb hope, but Jack opened the rift once, so maybe he can open it again,” Padalecki told Variety. “And Sam sometimes creates his own carrot on a stick to go after, so I think Sam, the way he grieves, is to go, ‘OK well, I’m going to focus on this and see if Jack can do this and guide him because I believe in him the way people believed in me.’ So we see Sam taking that route.”
How powerful is Jack?
According to Padalecki, “The Nephilim lore is that the Nephilim becomes more powerful than the angel who sired it. In this case that angel is an Archangel, Lucifer.”
Cas does come back, but is it the Cas they know?
Misha Collins has said that Castile’s return is a slow one - “He’s very dead … more dead than usual.”
“When he does come back as more than a lifeless body – we find him in a realm that we've talked about on Supernatural before but have never seen," he told Digital Spy. "He finds himself alone in this realm with only one other companion, who is another powerful being, played by a great actress."
Beyond the rift…
Last season we saw what a world without the Winchester brothers would look like – an apocalyptic hellhole. Executive producer Andrew Dabb says this season we will be seeing more of this world as it serves as an “on-going resource to really show the horrible difference in what the world looks like without these guys.”
And now that the show has explored arguably the biggest storyline – God – the apocalyptic world provides the writers with new creative avenues to mine.