Looks like the migration of legacy SPG hotels onto Marriott's reservation platform is complete: December 11th was supposed to be the day that the last four legacy SPG brands [St. Regis, Luxury Collection, Aloft and Element] transition over and I just performed a few searches across different hotels across the brands in different cities, and can confirm that the starwoodhotels.com domain is no longer appearing as a frame within the screen.
Done-diddly-un!
khabah