Probably not. There is no garauntee it will ever come out, since its actually a slightly larger drive (so I've heard) that might require the case to be slightly redesigned (not a lot, but enough to probably make apple question whether its worth changing). I suppose eventually it would have to come out, but I wouldn't count on it being in the next couple of months anyway.
I also don't see any iPod updates coming out at MWNY, since they just released the 10GB model not all that long ago. MWSF would be more likely. I would imagine that the 20GB iPod would be more money, unless they drop the price of the drives. Maybe the 10GB model would go to the price of the 5GB with the 20GB taking the 10GB's place.