Let me add that I'm now using the 'M' keyboard shortcut, that toggles between the read and unread states. It's a perfectly viable solution, whilst waiting for the UI in the cards.
I agree, the button to mark read/unread should be there.
I like the less cluttered approach of the "cards view". Take a couple-three lines to show subject, correspondent, date. But also include the needed button.
Please add not just the sender but the option of showing all correspondents in the Card View. This was possible in the list view. As someone who stores sent and received emails in the same folder this is crucial since otherwise I appear on all my sent emails instead of my recipients.