Why not???

Too much would be revealed about things in the series that are meant to be unknown at this time.

Frankly, I'm just not all that interested in Robert's Rebellion other than what's already been revealed about it in the books and the show.

Robert's Rebellion/Fall of the Targaryens would be cool, but so would Dunk and Egg/2nd Blackfyre Rebellion, First Blackfyre Rebellion, Conquering of Westeros by Aegon the Conqueror.

I can see your Cumberbatch, but not really the other two.

I have no good ideas on Lyanna. Perhaps someone like Saoirse Ronan if they dye her hair black. She has the long, pale face and beautiful features to play the part as well as the athletic tomboy aspects Ned says she sees of here in Arya.

I picture Robert being played by Tom Hardy if they can find a way to cover up the full body of tattoos. His performance as Bane in The Dark Knight Rises demonstrated he has that ability to dominate space like Robert really needs to. I just picture Robert as bigger than Butler is capable of playing.

Who plays a young Ned? That's the harder one for me...he both has to match Lyanna and look like he could grow up to be Sean Bean.

And Rooney Mara works as Lyanna