The future may well include legalization and acceptance of Marijuana, and possibly other-mood altering recreational drugs. And, as one post pointed out, there may be improved technology to prevent impaired driving.
I feel that, regardless of these and other future changes, the percentage of recreational drug users will remain the same. This is because a certain (and probably constant) percentage of people are genetically predisposed to be self-abusers. I would not expect the percentage to change. There still will be a majority who do not use, and disapprove of, recreational drugs.