Season 5 comes Jan 4, 2015 on PBS. Seattle is still the number one viewership of this PBS series nationwide. Here is what KCTS has shared with me.
Richard E. Grant (Girls, Gosford Park, Doctor Who) is joining the cast as Simon Bricker, who visits Downton Abbey as a guest of the Granthams. Anna Chancellor (The Hour, Four Weddings and a Funeral) joins in a guest role, playing Lady Anstruther, and Rade Sherbedgia (Eyes Wide Shut, 24) plays a Russian refugee. Returning guest cast member Dame Harriet Walter will reprise her role as Lady Shackleton, along with Peter Egan, returning as Lord Flintshire.-Mark Christopher
Also, I found this flyer from Alki Tours/West Seattle, offering fans a chance to go to Highclere Castle /Downton Abbey and many other Castles in England.