I'd like to see some guidance from HHS on what constitutes a justifiable rate increase.
That would be a good place to start.
As for threatening to exclude payers from participating in health insurance exchanges in 2014, I doubt it will have any effect on insurers' behavior today. Payers are no different from providers in that they are mightily challenged to implement systemic changes resulting from healthcare reform legislation. Who knows how high healthcare costs will be by 2014? The government's estimate that a 1% or 2% premium rate increase should be sufficient could be well off the mark.
If Sebelius is serious about keeping down insurance premiums, she's going to need federal legislation that pegs rate hikes to inflation or cost of living increases, or some other marker (unlikely). Or she'll have to enlist the aid of the 25 or so states that don't have the power to regulate insurance premiums, and let them do the heavy lifting. One way or another, she'll have to pull on some levers to get the changes she wants. Tough talk alone isn't going to cut it.