In comments to his latest post, GRRM provides some details concerning the remaining speaking roles left to be cast, the writing out of a minor part, and a list of non-speaking roles or features extras that are set to appear in the pilot:
A brief recap.
As of this writing, only three speaking roles remain to be filled. An offer is out on one, and we are waiting to see if the deal closes. Still looking for the other two.
The Nameless Eunuch has been written out.
In the pilot (though not, of course, the series), Rickon, Tommen, Myrcella, Ser Boros Blount, Ser Meryn Trant, Septa Mordane, Jory Cassel, Hullen, Vayon Poole, Jeyne Poole, Beth Cassel, and Hodor will all be non-speaking roles or “featured extras.” Some may not appear at all, or else will turn up only in the background. So don’t drive yourselves mad trying to figure out who will play those parts.