This is a great question, muppetwrangler! I've reached out for better clarity, I'll let you know what I'm able to find out.
carat and I have heard back from our team, and they advised that they have not been told date specific information, only that they'll begin adding stays at Delta hotels starting in February 2016. We tried to look for more information surrounding this on the Marriott website Delta_Marriott_Rewards_members: See frequently asked questions, but were not able to find a specific date in February on there either, so it looks like we're going to have to wait until we're closer to February to get exact information. Sorry for not being able to fully answer your question!