Massachusetts had the nation's highest rate of health coverage even before passage of a pioneering 2006 law requiring most residents to have insurance. Yet tens of thousands of people like Francisco Machado go uncovered each year and pay a fine. Starting in 2014, when much of the national Affordable Care Act kicks in, millions of other Americans could face a similar fine, putting Massachusetts in the spotlight as a possible indicator of what lies ahead for the country. The federal plan mimics the state's law in its basic approach to expanding coverage: Make health insurance more affordable through new subsidies and a state-run insurance market. Then compel most people to buy plans and penalize those who do not.