I take serious issue with this pronouncement by the director. For starters this kind of thing tramples on people's ability to form their own interpretations of a work.

Slightly less importantly, I think that this takes something away from the film. One of the fantastic themes of this film was how the replicants were more human than the humans. I mean it really shows the inhumanity of humans. To make Deckard a replicant means that you lose that contrast between humans and replicants.