Of course, my estimates and the CBO estimates could both be way off. It is possible that the exchange will be a big success. By roughly year 4 or 5 (2016-2017), a large number of businesses (if not all) would start providing their employees with vouchers to purchase plans on the exchange. The low-hassle nature of the public option and larger provider network could make it very popular. It would not be surprising if it were selected by half the people using the exchange. In this scenario, the public option would have closer to 60 million customers, instead of 6 to 20 million.

The problem with this whole line of reasoning is the assumption that people will want to move to the exchange in the first place. But there are no advantages to the exchange as opposed to traditional employer based health insurance. The idea that it will grow as you suggest is completely unfounded, even if it were instantly opened to the entire US population. The only real reason anyone cared about this was the public option tied to Medicare rates, which is now gone. Now it doesn’t even matter if they open it, because there is nothing good in there anyway. It’s now more like the Commonwealth Connector in Massachusetts.