Ain't gonna happen... not if the neo-prohibitionists (read: MADD) have anything to say about it.
They've managed to get the gub'mint to hold up highway funds (which promptly go into someone's pocket as a kickback
) to states who didn't raise the drinking age to 21, and then if they didn't lower the DUI/DWI threshold to .08 BAC. Don't be surprised if they push for legislation to lower it to .06 in a few years.