Lawrence Taylor, an expert (perhaps the expert) on DUI law, has an excellent post entitlted "The Future of DUI." Among many ominous predictions is this one:
The Past: DUI laws have always been a state-prescribed crime. With the prompting of special interest groups like MADD (Mothers Against Drunk Driving) and the desire of politicians to curry favor with voters, this has gradually changed. Using a "carrot and stick" approach with highway funds [South Dakota v. Dole, the famous Spending Clause decision, upheld this practice], the federal government has forced states to change their laws and penalties in such ways as: "per se" laws; .08% BAC; "zero tolerance" for drivers under 21; automatic license suspensions; standardized field sobriety tests; federally approved lists of breath testing machines.
The Trend: The federalizing of a traditionally state offense.
The Future: With the use of the Constitution's Commerce Clause, DUI laws and penalties will become "federalized". However, without the ability (or inclination) to arrest and prosecute these crimes in the federal courts, the states will be left to continue processing them in their own courts or administrative hearings.
If Congress did federalize DUIs, I suspect that things would get either much better or much worse for alleged DUI offenders. Federal judges would be miffed at having to decide DUI cases. Thus, they might actually start interpreting the Constitution properly, which would allow them to kick these cases out of court, or they might craft procedures designed to turn and burn DUI cases as quickly as possible. But given the states' current love affair with DUIs - which are great revenue generators for the state - I doubt they'll ever be heard in federal courts.
What I expect Congress to do is federalize the collateral consequences of a DUI conviction. That is, a DUI conviction will preclude someone from obtaining many of the licenses issued by federal agencies, and a DUI conviction will likely prevent someone from obtaining federal employment.
Anyhow, for you should read the whole post, for predictions from someone who actually knows (instead of, like me, who is merely speculating) the path of DUI laws.