Goldman never really seemed like a great choice to me, she's written some decent stuff with Matthew Vaughn(original Kickass, first Kingsmen) but its all been very self aware which in general GOT wasn't.
One thing that always stood out for me was the talk that Watt's character was a "socialite" when you get the impression that the Age of Heroes is a much earlier society than we see in GOT(more late medieval mixed with some early modern).
That kind of series to me is not something you rush out to order, it would really need very extensive planning in terms of the detail of the setting and the larger story probably over several years.