Another data point. I also got the email canceling my flight back to the US on the 8th. Like others MMB showed red “subject to possible disruption”. It let me change both flights so now I am leaving a day earlier and returning on the 7th. I have the email confirmation from BA already. And a sympathetic Marriott agent helped me drop the last night from my existing reservation without changing what is now a pretty good rate.
I made the changes on the web about 4 hours ago. Did not have any trouble and was offered both BA and AA flights.