what would be cool, I know they have to finish this story in like 7 more seasons first, and Im sure they wont ever do it but what if they made another series about roberts rebellion and the fall of the targaryens?
There were some industry rumors that when Charlize Theron offered to play a role on GOT for free ( well not for free, but for minimum rate), that HBO execs asked Benioff and Weiss if they could shoehorn her into a small cameo. I think the role of Lyanna Stark was on the table for discussion, as it would be a flashback/non series regular role.
To my understanding Seth Green tried very hard to get a role on the show. Lots of celebrities are GOT diehards. The problem of course is a celebrity who is too well known would be jarring for the audience to see.
In probably the saddest bit of casting news, apparently Amanda Peet has been lobbying hard for a role at some point and some time and there's a chance she might get one.
It's interesting though, within the culture of the universe, that Ned Stark and Robert Baretheon were probably better suited to be bannermen themselves. Ned only took Winterfell because of the line of succession made it so. By having Neds father and older brother burn, the Starks lost the political capital of having Ned marry a politically reliable choice to secure the family. I think this also keys into the fuel for Tywin's anger at Tyrion. Not only was he seen as an embarrassment, but the death of his wife meant there would be no more sons or daughters to marry off as political capital.