In the years since Harry Potter came its end, Radcliffe has played Allen Ginsberg, a demon, a farting corpse and, most recently, an undercover agent posing as a white supremacist.
I don’t know there there are any areas of Westeros that are too extreme for the actor at this point in his career.
I know one is supposed to find the best actor for a part, and not necessarily the other way around, but David Benioff and D.B. Weiss can easily figure out a character to introduce for Radcliffe, who has gone as far as any entertainer ever has in avoiding being typecast for onscreen roles.