I decided on August Diehl as Deckard, with Zoe Saldana as Rachael (I think it'd be a great challenge for her). Sticking to Ridley's portrayal and notion of Deckard being a replicant (some fans I've found don't), I made this:
I thought of Christoph for Tyrell, actually. The creation and eventual fate of the replicants is heartbreaking to me, and his abandonment of Rachael after she realized she wasn't human was cruel. However, Tyrell, even when confronted by Roy, treats them (as they are essentially his children) so warmly. It's quite malicious of him, though that never shows. I think Christoph can easily play that: charming, and nurturing, though ultimately, he's a villain.
I was thinking of Eva Green as Zhora and Ken Watanabe as Gaff (aside from Batty's dialogue and speech, the line, "It's too bad she won't live; but then again, who does?" is one of my favorites and I'd love to hear him say it. And make origami unicorns).