According to GRRM this painting is very close to how he envisions the Iron Throne: 
“ The HBO throne has become iconic. And well it might. It's a terrific design, and it has served the show very well. There are replicas and paperweights of it in three different sizes. Everyone knows it. I love it. I have all those replicas right here, sitting on my shelves. And yet, and yet... it's still not right. It's not the Iron Throne I see when I'm working on THE WINDS OF WINTER. It's not the Iron Throne I want my readers to see. ”
“ The way the throne is described in the books... HUGE, hulking, black and twisted, with the steep iron stairs in front, the high seat from which the king looks DOWN on everyone in the court... my throne is a hunched beast looming over the throne room, ugly and assymetric... ”
“ But [Marc Simonetti] has come closer here to capturing the Iron Throne as I picture it than any other artist to tackle it. From now on, THIS will be the reference I give to every other artist tackling a throne room scene. This Iron Throne is massive. Ugly. Assymetric. It's a throne made by blacksmiths hammering together half-melted, broken, twisted swords, wrenched from the hands of dead men or yielded up by defeated foes... a symbol of conquest... it has the steps I describe, and the height. From on top, the king dominates the throne room. And there are thousands of swords in it, not just a few.