HBO has continued to push forward the story of Game of Thrones when the main series has already ended. George R. R. Martin, Game of Thrones maker, stated on his blog that some yet-unannounced names have joined the list to develop a fifth concept.
“We had four scripts in development when I arrived in L.A. last week, but by the time I left we had five. We have added a fifth writer to the original four. No, I will not reveal the name here. HBO announced the names of the first four, and will no doubt announce the fifth as well, once his deal has closed. He’s a really terrific addition, however, a great guy and a fine writer, and aside from me and maybe Elio and Linda, I don’t know anyone who knows and loves Westeros as well as he does.”
Source: George R. R. Martin