As someone who's never read the books and has no intention to do so, I think George will eventually finish The Winds of Winter - around late 2020/early 2021 is my guess - but never A Dream of Spring. From hearing the words of people who love both Game of Thrones and A Song of Ice and Fire, they're frustrated and a little sad that the adaptation wasn't able to continue beyond season 5 and that the transition to original material hasn't always been a comfortable one for them to watch - but despite their feelings about D & D, they find themselves more frustrated with George for expanding in books four and five when he should have made more of an effort to do what the show has done, which is narrow things down and combine various plot strands for effiency's sake.
I haven't read the books so I'm a little biased, and a little ignorant as well, but I'd much rather take the show's version of certain plotlines than the book ones. I'd rather see Sansa go back to Winterfell and be placed in the hands of Ramsay Bolton than be forced to care about Jeyne Pool, who Ramsay thinks is Arya Stark but actually isn't. And I'd rather see Mance Rayder burned alive by Stannis than see the show try to pull off that it's not Mance Rayder but actually Rattleshirt in a magic mask. Conversely, I'm eager to see where George would have taken Arya's Braavos plotline, which was clearly preparing itself to be something much bigger and more complex at the end of season 5 but was ultimately boiled down to Arya vs. the Waif with Jaqen playing referee, and how Daenerys' eventual invasion of Westeros would have played out. I can't help but think she'd have gone to Dorne than Dragonstone.
I think we'll eventually get answers to some of these questions, but not all.