To me it's always been clear that Deckard's a human. Deckard has human memories, which would make him a Nexus 7, like Rachel. No one at any point indicates that Deckard is a hugely expensive prototype replicant sent out with a license to kill. Who the hell would sign off on that?
Deckard also gets his butt handed to him by Pris, a pleasure model and he's helpless against Leon and Roy. Again, who'd send out a hugely expensive prototype to hunt beings that can tear it apart like a rotisserie chicken?
Why would Gaff bother saying "It's too bad she won't live!" if he knows Deckard is a replicant? He'd surely know.
Not to mention how the point of the story falls apart if everyone's a replicant. You get no "What does it mean to be human?" question, you get no contrast between a man whom the years have not treated kindly and the replicants who would take those unkind years in a heartbeat just to live a little longer.