The age-old question of whether or not Deckard is a Replicant has been debated for the past 34 years, and no less by the Director of the original (Blade Runner) Ridley Scott, right up to the Director - Denis Villeneuve - and writers - Hampton Fancher and Michael Green - of Blade Runner 2049 .
Specifically, Green and Fancher both agree that this topic should stay ambiguous, and that's how they've both written it, as they've said in a recent interview with Josh Rottenberg (Los Angeles Times) :
Josh: As I see it, this movie seems to suggest that Deckard is a human, not a replicant. But there are other people who interpret it differently.
Green: One of my favorite outcomes from the film from early reactions I’m seeing is that people are coming out of it even more sure of the opinion that they’ve held — and still not agreeing. That gives me tremendous joy. And that includes some of the people that were responsible for the original film and this film. The debate seems to continue, and people seem to think that those who think the opposite of them are nuts.
Fancher: I’ve always thought that if the replicant-cy is a success, then you don’t know that you’re a replicant. So either way you’re … in terms of the ambiguity of it — and life is ambiguous.
Deeming Deckard a replicant closes the door on the party: “Go home, everybody, it’s closed.” It’s got to be up in the air or there’s no dog fight. It’s an aesthetic philosophical equation. Like, I’m not so sure Michael Green is an authentic human being. You know what I mean?
Green: I agree. I don’t think this movie answers definitively one way or the other, but I’m tickled that many people do and I’m also tickled that many people don’t. Some people come out saying, “Thank you for not answering it” and other people come out saying, “Thank you for answering it.” And that’s what we set out to do. We wanted to make sure that the ambiguity is built into the story.
“Blade Runner” is all about questions of authenticity, comfort with ambiguity, and you can’t discuss the film without talking about that particular ambiguity — is he a human or a replicant? — or even about which version of the film is the authentic version of the film. So the film itself is representative of gradations of realness.
-Los Angeles Times, 2017-10-09, Is Deckard a replicant? 'Blade Runner 2049' writers discuss that and other mysteries, by Josh Rottenberg
Fancher and Green's stance on the matter (how it should remain ambiguous) is also elaborated in another recent interview with Adam Chitwood (Collider):
Fancher: “Yeah, I always [believed] he’s not a replicant. I thought if he’s a replicant, the game’s over. I think he doesn’t know, also. So to make him a replicant—Ridley from the beginning [said] he’s a replicant, and I from the beginning said he’s not, or we shouldn’t know if he is, I don’t know if he is. The press has always asked me, I don’t know. And when Ridley put in the ostensible evidence that he is, the red eyes or whatever, in Blade Runner 1 I didn’t like that.”
Green: The fact that it’s a question is what’s important. The puzzle of Blade Runner, one of the many reasons it’s the classic it is, is that the chasing for authenticity is both baked into the narrative of the story and the meta-narrative of the film that there is no authentic answer to that question. Which just meant that telling the further story, that had to be baked into the story as well, that everyone who watches it has that question of which version should I watch, what does that mean, and the answer is you don’t get to know. Generally American audiences are very uncomfortable with that level of irresolution. Blade Runner challenges that and it’s not just an American favorite, it’s a global favorite.”
-Collider, 2017-10-09, 'Blade Runner 2049' Writers on Whether Deckard Is a Replicant, by Adam Chitwood
Furthermore, Director Denis Villeneuve, has said in a recent interview with Marcus Errico (Yahoo Entertainment):
“I know Hampton believes [Deckard’s] human, and Harrison believe he’s human, ... I went to see the film with Ridley when it was playing in London on Imax and after it ended, he turned to me and said, ‘See, now you know that he’s a replicant,'... I said, ‘OK, Ridley, it’s your film, you can think whatever you want.’
“But as a fan of the original film I enjoyed the ambiguity and I did not want to ruin the mystery for fans.”
-Yahoo Entertainment, 2017-10-10, Is Deckard a replicant? Director Denis Villeneuve explains how 'Blade Runner 2049' handles the great debate (spoilers!), by Marcus Errico