The McCarran Ferguson Act exempts insurance companies from Dept. of Commerce regulation. They are regulated by the States they operate in. Hence they can sell you pretty much anything the State regulator says they can sell. The federal government , however, can determine which policies qualify for federal subsidies and tax breaks. The federal government can also determine which policies will exempt a person from paying a penalty and the amount of the penalty.
Without repeal of the McCarran Ferguson Act, I don't see how the federal government can achieve its cost and participation targets. It seems there are serious flaws here, and I can't understand how depending on competition between companies to achieve affordable rates, even assuming the participation targets are met, will work well as long as the McCarran Ferguson Act remains. Furthermore, when the court "teaked" the ACA by allowing individual States to opt out of medicaid expansion, that really threw a monkey wrench into the intended mechanism for getting minimum wage, single-no-dependents, and long-term unemployed covered in the non-participating States, i.e., the Deep South. (I am not clever enough, I guess, to see how this thing can work without bringing insurance company regulation under the Department of Commerce, and that would require repealing the McCarran Ferguson Act. Although that would seem impossible given the current House make-up, nothing is too bizarre to contemplate.