I kinda feel like two more seasons won't be enough considering how large
The Winds of Winter and
A Dream of Spring will likely end up being, but considering how much fat GoT trimmed off of
A Feast for Crows and
A Dance with Dragons these past two seasons, it could be doable. Not surprised HBO wants eight, though.
I'd love to see a miniseries about Robert's Rebellion after GoT finishes, and the Dunk & Egg tales would be great candidates for like 90-minute TV movies or something. There are some other Westeros stories I think would make for interesting miniseries, too, like something focusing on a young Tywin Lannister and Aerys Targaryen, their friendship during the
War of the Ninepenny Kings and then their falling out after the
Defiance of Duskendale. And the
Blackfyre Rebellion would be a great story to adapt, too, IMO.