Personally I think the whole point with Ridley saying Deckard's a Replicant is only from his perspective, and not necessarily that of PKD. Granted Ridley is the Director, but that doesn't necessarily make it so. That simply makes his statement true for
his vision of the film and character. It's also a bit funny that it took so long to get a definitive statement for something he seems to feel so strongly about.
I do not believe the reaction to, and significance of Roy's amazing rescue of Deckard at the end would have had the same emotional impact with Deck as a Replicant. Roy needs to put away his disgust for humans and save one to truly show his evolution, valuing any life as his own was slipping away. Reading DADoES makes me think he is not a Replicant.
In the Blade Runner fanfic I am writing here:
http://bladezone.com/phpBB2/viewtopic.php?t=2470
I will be exploring this theory of my own as the story unfolds further:
The Tyrell corporation realized the dangers of Replicants who, at the end of their lifespan, have come back to Earth to attempt a life here. They can't afford to have Replicants, their products viewed as dangerous to the general population. As a result, the Tyrell Corporation has the police department bought and paid for at the very highest levels. They are aware of Deckard's unicorn dream from either his very own VK test and a question about recurring dreams, or perhaps it was mentioned to Holden at some point in Deckard's Rookiee training under Holden.
Dave Holden, being the good cop he is, would have told Bryant if asked questions about Deckard. Gaff presents the chicken origamy to put doubt into Deckard, worrying that he might not have what it takes to come back as a Blade Runner, that he might have become a "Chicken head" (from the book). The Unicorn origami is presented by Gaff after he leaves Rachel alive, KNOWING that Deckard will flee with her. It is used to plant the suggestion to Deckard that he might be a replicant in order to force his hand and make him flee with Rachel.
This is something the Tyrell Corporation wanted. That way, the corporation can more closely study the behavior patterns of the Nexus 6 line with an unrestricted lifespan and test both the memory implants and Rachel's ability to improvise and adapt to the newfound knowledge that she is indeed a Replicant. It is also a great opportunity for them to gather data on how she interacts with a human on a rapidly growing emotional level.
They are also studying Deckard, struggling with his human thoughts and emotions over the suggestion that he might be one, and how he relates to Rachel. This way, they can either tweak the Nexus 6 line, or create in the Nexus 7 models a more highly evolved emotional matrix, even further blurring the line between human and Replicant.
The entire escape of the Replicants, their journey to Earth, and the involvement of Deckard and the Police was orchestrated by Tyrell to put this plan in motion. In the words of J.F. Sebastian, "He's a genius."
Study history. Dangerous events are allowed to unfold all the time as a catapult to public response and retaliatory actions. What a fantastic experiment the whole film becomes.
It's just an idea, but one I want to play with. If you haven't read the start of my story, I'd love to have you check it out and let me know what you think so far.