So... the update is out and we could take a better look at their new bipedal design XD. I kept the tail from the Kingdom version, made some color palette changes and made the arms longer because they were so short they actually looked goofy xD, but in general I like the bipedal design, I guess that's a consequence of being a furr-
The redesign wasn't justfied by the game and they were already depicted like that in petroglyphs, so even before the update was out I came up with a headcanon:
The quadrupedal version was their original dragon form, but they became so attached to cookies over the centuries and strengthened their bond with them so much that it ended influencing their dragon form during their reawakening, making it become bipedal and resemble more their Cookie form even as a dragon.