Marriott did a deal with both Chase and American Express for credit cards. Chase gets the bulk of the personal business, but American Express gets to issue a premium personal card. American Express gets the small business cards. And cardmembers keep their legacy products.
Both banks are issuing new products, and making changes to existing card products too. So in addition to speaking with Marriott about the changes I reached out to Chase and American Express as well to learn more and they were both forthcoming.