GRRM recently said that none of the 4 series in pre production are Dunk and Egg or Robert's Rebellion.
1) He wants to write numerous Dunk and Egg novellas without a tv show overtaking again
2) Everything worth telling about Roberts Rebellion will be told in ASOIAF/GOT
Im super keen for a general World of Ice and Fire anthology series, with stand-alone episodes and 2/3/4 parters (i imagine something between Black Mirror and American Horror Story)...
The "Broken Man" episode really stuck out in how well they created this self contained story (of course, we have the Hounds backstory and it will lead into more things, but it works just as well on its own).
One episode on the streets of Bravos, the next a 4-part series on the Dance of the Dragon, then a maester in the citadel narrating the apparent history on Asshai or Old Nan narrating the Age of Heros.
You can give writers and directors heaps of creative freedom because there is no strict style to stick to. I think thats the best they could do...