Marwyn may not be a major game-changer in the books at this point, but Jim Broadbent is such a venerable actor that it would have been a waste if he only popped in for a scene or two.
Even if his scenes aren’t huge, he’ll evidently be a fairly important character, which actually isn’t a total surprise.
Given that Season 7 will reportedly only run for seven episodes rather than the usual ten, Jim Broadbent is slated to appear in more than half of the season.
Broadbent also mentioned that he spent a lot of time filming with John Bradley, so we can bet that we’ll see plenty of Sam and this archmaester interacting at the Citadel.