Well we know Thor is the big bad in this entry (at least as far as they've told us). I'd assume Odin would be the major enemy of any final Norse God of War game?
I've also wondered ever since the Loki reveal, how it will figure into things that Loki becomes seen as one of the Aesir, as a trickster brother of Thor and adopted son of Odin?
A theory I had at one time or another would be, Kratos dying in this game, and Loki somehow being taken is as an "Adopted son" of the gods (I.e. held prisoner etc). So the final story would be Atreus/Loki just getting revenge on all the gods?
But if this 2nd game is already potentially "Ragnarok" then maybe all that would happen in the one game? Who knows?
The other popular theory for a while has been that Kratos IS Tyr, given they're both Gods of War, and Tyr was said to have traveled through time and to many other cultures and mythologies. So another thing I could see is it LOOKING like Kratos has died but perhaps been sent back in time or something.
There's already some weird time travel stuff in the first GoW, since we know in mythology the World Serpent is Loki's son but Atreus is still a teenager.
TBH seeing how they continue to weave all this mythology in with the the momentum of their storytelling is the thing that has me most excited. I loved that Loki reveal more than anything else in GoW, so very invested in what that is building to. But I think I would be disappointed if, in the very least, it didn't lead to a dual protagonist situation in this or future games (Or at least a Loki spin off). Would love to see adult Loki/Atreus fighting the gods.