Journey into Nyx previews are coming up soon, but with the set release almost an entire month away, one wouldn't expect the Product Information page to say anything particularly revelatory. But the banner above the Journey into Nyx Product Information on magicthegathering.com notably has some never-before-seen art.
Specifically, we're looking at roughly the top one-third of the piece, which is a close-up of an armored Harpy apparently swooping into battle with a sneer on her face. She's drawn more humanoid and more expressive than any of the other members of her species in this block, and the artwork is really zoomed in to her expression, plus her armor looks unique in its whorled design in bronze and bluish jewels.
In other words, this might be the first legendary Harpy creature in Magic. Given what colors Harpies are in Theros block, she's definitely blue, but white might fit as well given her general look. It's possible that this is a Chorus of the Tides-style "civilized" Harpy with heroic. Alternately, she might be an enchantment creature, with either bestow or a new mechanic for the last set, and we simply can't see her Nyx starfield because it's in a portion of the art that's been cut off.