I'd rather be shooting up bandits with my robot buddy in Borderlands 3, but here I am.

Friendly reminder to those who seem to have forgotten: Zenos' whole plan is to mantle Zodiark the way he did with Shinryu. Consequently, whether Zodiark is "good" or "bad" depending on perspective is, as far as I can figure, a complete nonissue. Further, with his "heart" imprisoned elsewhere (i.e. functionally dead), even if he were made complete again as far as I can figure he'd be either braindead or a mindless, rampaging beast. While Shadowbringers did paint a more benign picture of Zodiark (the threat he poses to mortal life was an extension of the Ascians' will; we don't know what he actually wants or even if he wants) that doesn't mean he's "good" or "on our side." In Zenos' hands his power is without a doubt very bad news bears, and I have little reason to doubt Zenos' plan will come to fruition.

Conversely, Shadowbringers painted Hydaelyn in a more ambiguous light than she'd been before, but that doesn't mean she's a malign force in the world. Her raison d'etre is to keep Zodiark's power in check, including preventing him from consuming extant life as fuel. Telling us a falsified (or rather half-true) account of the origin of her conflict with Zodiark doesn't change that, and she hasn't shown any malicious intent toward the people of the Source or Reflections - on the contrary her whole goal, so far as it's been shown, is to keep them from dying. That doesn't mean she can't do wrong or has never done wrong, but there's been no sign of anything malign coming from her.

There are two important-looking bits in the 5.5 trailer that haven't been touched on yet - the PC meeting the figure of light on Silvertear's shore, and Zenos stating that "[He] will await us on the darkened Moon." I'm expecting both of those to inform a lot of what's going on in 6.0, so I'd strongly suggest waiting for those before deciding who is on what side. I'd also suggest hedging your bets considering, as I remember, Yoshi-P said Endwalker was going to be a more straightforward epic tale.

P.S. "Source glows a dangerous hydaelyn blue?" Pretty sure that's the sun, or if you're talking about in the end the planet being eclipsed by the moon. Either way the trailer opens with an ominous shot of the moon, and near the end associates Zenos with said moon by zooming in on his eye and fading his pupil into it. PLD being on the moon doesn't have any symbolic significance by my reckoning, and it's one of the most straightforwardly heroic and light-associated classes in RPG history. Just... Saiyan.