The only thing I could realistically see happening is the "Roth" type plans being closed to new money. In other words, what was contributed under today's rules would be grandfathered in, so to speak, and the money, of course would remain tax free and under the control of the individual.
I think the real misfortune is how few people who are eligible contribute to an IRA or 401K plan. The statistics I have seen on the personal savings habits of Americans are quite discouraging. All too many people can't seem to manage their money very well, though I also realize that for many people to just make it from paycheck to paycheck is a genuine struggle through no fault of their own.
I am hopeful that the "Roth" type investments are something everyone, liberal or conservative, D or R, could see as a good option to have available. The left has no grounds to view it as a tax shelter for the very wealthy and privieged while the right can particularly appreciate the strong positive incentive it gives to the individual to take personal responsibility for planning and saving for ones future needs.