In his last post on his blog he said:
"THE WINDS OF WINTER is very late, I know, I know, but it will be done. I won’t say when, I’ve tried that before, only to burn you all and jinx myself… but I will finish it, and then will come A DREAM OF SPRING."
Now he gives us a deadline. One that could potentially burn us and jinx him. And even if it's not really a deadline, he knows his fans are going to rabidly grasp onto it.
He is either confident he is nearing the end or, despite declaring otherwise, hasn't learned his lesson.
I really hope it's the former.