Very possible in the DC circuit. However, there is a similar case in the 4th circuit and most observers think that will go the way this one did with the panel. That would result in conflicting rulings in the circuits and a certain trip to the Supreme Court.
Basically, the Supreme Court would have to conclude that the IRS has the power to supersede the clear language in the law which says that subsidies can be paid only to people who have signed up for state exchanges. IRS does not have that power.
Yikes, just saw an article saying the fourth circuit ruled the subsidies to be legal. So if the DC circuit overturns the panel there is no conflict among the circuits. :-(