I think voting will depolarize eventually, and will be based more on economics. Whites will be about 50-55% R (WASPs vs. blue-collar voters), blacks will be around 75% D, Hispanics around 55% D, and Asians about 50-50.
Don't think you can pinpoint white voters that easily. Will the WASPs be Rs and the blue collars Ds, or vice versa? There are economically conservative, Christian evangelical WASPs along with the academic, Northeastern liberal WASPs. With blue collar "ethnic" whites (basically myself) there's religious vs. secular. I agree blacks and Hispanics will be less D in the future and I know the GOP will cool it on the immigration rhetoric. They pretty much gain a large number of Hispanic social conservatives if the anti-immigration stuff dies off which is simple and scary for us Dems, but will the Teabaggers let the GOP do it?
