For the record, I've always hated the idea of Deckard being a replicant. I am trying very hard to allow myself to accept that this interpretation is fine and can coexist with my preferred version of events. Needless to say, I find it extremely difficult. But in the spirit of fairness and with the cruel onslaught of empirical reality mocking my every cherished belief in the matter, I must now concede there is pretty much absolute, unambiguous, undeniable confirmation that if you watch the versions of the film where Deckard has the unicorn dream/reverie while sitting at the piano, the scene in question stands as irrefutable proof that Deckard is a replicant. Ridley Scott said as much in a 1982 interview with Starburst magazine in an article entitled The Blade Cuts:

Ridley Scott: Did you see the version [of the script] with the unicorn?

Alan McKenzie: No.



S: Sure. To me it's entirely logical, particularly when you are doing a film noir, you may as well go right through with that theme, and the central character could in fact be what he is chasing.




Via Blade Runner Insight