They've the power to add taxes to 401(k)/IRA withdrawals in the future. I think it's unlikely - it'd be political death to whoever proposed it - but it's theoretically within their abilities.
They could realistically change the tax structure or even the retirement age(s) at which you could withdraw the funds. But if there were another mega-stressor to the financial system in the future, it seems that this pool of trillions of dollars would be ripe for the picking. Let's face it, lobbyists get what they want. Not the people. So if the bank's risky investments cause a panic and the only thing preventing an economic meltdown is the re-purposing of 401k funds....well...
I highly doubt it would be that direct. A realistic way to do this would be to change the tax structure based on age. Meaning, the only way to extract the money without incurring severe penalty would be to do so after some advanced age. Then put in place a rule that any funds left after death become part of a new social security style safety net. Likely for the ever-increasing number of baby boomers who are retiring and living longer than ever.
Yeah, that's my point. You're talking about a retirement plan that impacts retired people who vote in droves. For the considerable future, those retirement age people will be baby boomers. They also happen to run the government. So why would it be unreasonable to expect them to pass laws that are favorable to them during their retirement as opposed to our retirement in 20/30/40 years.
