But larian tells us he is one of the absolutes chosen and we see him talking to Ketheric ...then there's no mystery. There's absolutely no reasons for the players to ever trust him. There's no cool reveal ingame when the clues finally tell us he is the villain.
Yes, it’s interesting that Larian clearly don’t think that they need to keep his allegiance under wraps in order for his story to work. I hope they’re right. I like uncovering a mystery and hidden motivations in a game, but I do think a game that’s aiming for replayability (as I hope BG3 is) can’t rely on it too heavily as the surprise will be lost by the second run. Fingers crossed there’ll be interesting motives that might tempt some characters to cooperate with Gortash, at least temporarily, even though they (or at least we) know he’s with the Absolute.