I'm thinking pulling in the likes of Janina Gavankar (already done some HBO) as a sandsnake. Also thinking someone like Seychelle Gabrielle as a younger Sandsnake (like Sarella/Alleras).

And of course, Edward James Olmos as Doran Martell.

Accent wise, I was almost thinking an aristocratic accent from the old genteel North or South Carolinas. To my ear, it always seemed to be one of the closest of American accents to the British ones, just a slow drawled out version of Received Pronounciation or such.