The advantage of a 401K over the Roth is that since both can be raided, at least with the 401K your money is being taxed only on the way out. With the Roth you are being taxed on the way in for sure, and you run the risk of it being taxed on the way out as well.
Judging from the past my guess would be that we wont see something as obvious as a penalty or a fee. Instead what you may see is a more aggressive required minimum distribution schedule. Perhaps you could see the date of penalty free withdrawal pushed back from 59.5 to 65 or 67 years of age. Means testing of social security benefits has been mentioned before. If that gets put in place, and you fail the means test for social security, they will have effectively taxed you more your entire working life.