We pretty much do know what the choice is ultimately about, as the game spells it out a few times throughout already: The MC has to choose between saving or destroying the world. And while there are nuances to what "destroying" the world might mean they are pretty much all basically evil. I don't think there's any variation of that potential outcome that is even morally gray. Now how much we can flip-flop around is unknown...we can completely flip like a lightswitch at the end of Season one but can we keep doing that in seasons 2 and 3? Could we in theory play all evil until the end of season 3 and still save the world or all good and still destroy it? That we don't know. But in terms of the endings each path leads to, those are pretty straightforward.
The issue I see with this though is that it'd be very hard for such vastly different endings to feel genuine if 99% of the story was mostly the same up until then. And I don't seriously see two full seasons of essentially completely diverged narratives, and likely not even one season. The amount of extra work that would require is massive.
Now, if "destroy" is used loosely here or an unintended consequence, I could maybe see something. But the amount of character divergence that would be needed to separate a heroic MC from one that would willingly destroy the universe in the most direct sense doesn't seem like something that could just be handled by occasional minor branches.
Maybe I'll be surprised though.