If I was writing the finale and endgame...
So, I’ve been trying to put down my thoughts and speculation and ended up with way too much speculation for it to all be true, I mean, who knows if even some of it is at this point, the beauty of this season is it is full of misdirection and missing information so it’s so hard to tell what is likely.
I just ended up writing down some conjecture for what I believe makes most sense and what I would do if I was writing it from here on… Full disclosure I’m totally aware that some or all of this may not happen, but it’s what I want to see happening and what I read could very well most likely happen based on current info…
You know me, its all pretty much rainbows and unicorns ;)
The nephilim - is neutral / good, will end up bringing balance to the universe.
It will be raised by Dean, the “righteous man” while Cas is separated from them. By next season it will have exponentially grown and by next season finale it will have aided the demise of Lucifer, again reiterating that blood does not tie you to family or dictate your life choices and how ironic that the nephilim would be Lucifer’s demise while Castiel is his mirror and is the one who helped show the child the goodness in Humanity and the word.
Cas & Dean & Destiel - at the moment Dean is blinded by love / worry and mistakenly thinks Cas isn’t himself (there’s a lovely mirror to this in 12x10 that I expand on below). Dean will not trust him at first in the finale, because he thinks Can is not himself, perhaps with Sam they will try to go against Cas to remove the nephilim’s grace, but Dean will be convinced by Cas in a reversal of season 4′s end.
This is Cas’s culmination of his depression / self worth arc - he will be the hero in this story, the one to convince the others of the “right thing”, save the child and eventually bring balance to the world (this is what I believe the child showed him, not a prophecy as that takes away the concept of Free Will, but a goal to aim for). This will leave Dean to raise the nephilim on the “righteous path” while Cas is probably separated from them due to cosmic consequences or other for the first half of season 13.
Dean needs to have the “winning him back” romantic trope arc after the “break up” - Dean has to face the fact that not facing his feelings are what got Cas ‘taken away’ in the finale or at least meant that Cas was taken away not knowing how he feels. This whole season has seen Dean be more honest but he is still withholding his feelings from Cas and there must be a consequence to this.
Personally I do not see an “I love you” in this finale, perhaps a singular “I want you to say” rather than the “we” as this is a recurring theme now and some development must come forwards for sure, but I think it’s too early for I love you’s and we need Dean to be still searching himself in early season 13. His self acceptance arc is nowhere near concluded yet (unless something DRASTIC happens in 21-22).
Perhaps Cas is taken away (perhaps with Mary?) to a place where time doesn’t exist? So they are not suffering but DEAN IS. Dean has to face his feelings and the consequences of not expressing them. The General Audience needs to see this from him.
Basically I can see how this really now could if they wanted to, all head towards a really positive endgame with the nephilim as a bringer of balance, endgame TFW as hunter/mol leaders, Saileen, Destiel and many other positive aspects that I feel the narrative this season lends itself to far more than a negative endgame.
Expanded below the cut why I feel this way as it got a bit long :)