I made the switch yesterday. Like OP, I am Hyatt Diamond and Marriott Gold, and also like the 4pm checkout. My travel next year is taking me away from enough Hyatt cities that I can't qualify under the new rules. Seems silly to try anymore when there is always a Marriott down the street. I enquired about a platinum challenge and Marriott responsed very quickly. Will be Platinum in December after 9 more stays.