This is how the IRA cap would work, from what I read:
you save the maximum in your 401k, invest wisely over your 35-40 year career. It ends up with more than $3M. You roll it over to an IRA so you can have direct control of the money and how it is invested. Presto, with this law change, you must immediately withdraw all monies in excess of the cap, and pay the highest possible marginal tax rate.
Next year, the cap stays at $3M. The stock market is up 20%, you must immediately withdraw all your earnings and pay the highest possible marginal income tax rate.
Punish all producers who have the gall to attempt to earn more than the $200k/yr that the government thinks is enough for you.
Thanks for the explanation.