Next step in health care - rationing by availability

Now that the enrolments of US citizens under the Affordable Care Act are finally rising (albeit slowly) it seems that the next challenge for participants once they can afford the payments will be finding a doctor who accepts their insurance:

Independent insurance brokers who work with both insurance companies and doctor networks estimate that about 70 percent of California's 104,000 licensed doctors are boycotting the exchange.
Mazer, a past president of the San Diego County Medical Society, agreed, saying, "I cannot find anybody in my specialty in the area that has signed a contract directly with any of these plans."

It seems as if the way that insurers on the California exchange managed to make premiums as (relatively) low as they were was by dropping reimbursement rates; consequently, a large number of doctors aren't going to be playing. They already have plenty of business with customers via employer plans that reimburse at acceptable rates, why should they drop their rates for other customers?

By the middle of next year the effect of the Affordable Care Act plans on regular customers should be clearer. It'll certainly be an improvement for people with preexisting conditions who couldn't get insurance, but it seems that an awful lot of people forced onto the exchanges will be paying more, for plans with higher deductibles, and yet will struggle to find a nearby doctor who will accept them...

Eventually if there's enough of a market I'd expect more doctors to come in and open up large treatment centres to make economies of scale and provide OK-if-not-great care at lower rates, but this rather depends whether the hassle of dealing with ACA regulations and insurers is going to make it worth their while...

(The next "logical" step if this turns out to be a problem is for the government to force doctors to accept ACA exchange insurance rates as a condition of practice...)