Here is what will happen. The feds will hold hearings on this matter and then figure out a way to start fining employers who do this. You watch.
As I understand it, as the law now stands, this is perfectly legal to sidestep the penalty by cutting employee hours down below the threshold, and this scenario was certainly discussed and mentioned prior to the law's passage. Now it is actually happening. Duh... Surprise! And the still unanswered question is: If a worker can't afford health insurance premiums at 40+ hours/week, how are they going to be able to afford health insurance premiums at 29 hours/week? The answer is that the worker will pay the tax penalty when they file their return. The tax penalty will still be cheaper than the insurance premiums.
Something will hafta happen. I just don't know what it will be. Maybe Congress will raise the minimum wage to $15.00/hour?