[Does GRRM plan to write any stories concerning ancient Valyria?]
Not at present, but anything is possible in the future.
[How about young Robert, Eddard, and the War of the Usurper?]
Not at present, but I never say never.
[Will Roy Dotrice return to reading the audio books?]
I would love to have Roy back, and I know he'd love to do it. It all depends on the schedule, and whether or not he is available when Random House wants to record. Last time there was a scheduling conflict.