The DNC has proposed a wealth tax every year since 1994. It never gets out of committee. 15% of your retirement account (any type).
That would have to be 15% of the income attributed to the account. 15% tax on the account would confiscate it in roughly 7 years.
Of course, that would go back on the whole promise/premise of IRAs, SEPs, and Roth accounts. A slightly lower tax rate wouldn't be enough to induce me to fence off my money for several decades.