Kylie Jenner just boarded a private plane to her birthday yacht party with a very interesting piece of luggage ... a garment that certainly looks like a WEDDING DRESS ... but TMZ knows otherwise. Also Ryan Seacrest was weirdly left out of Disney's press release announcing a new season of "American Idol" -- but we've learned he's not out, just delayed with the Mouse House ... on account of what looks like a massive new deal.