Rookie QB Nick Foles had a tremendous preseason debut, backup Mike Kafka broke his left (non-throwing) hand, and suddenly people are asking: Why not Foles backing up Michael Vick? The question carried extra weight after the game when Vick’s injured thumb raised issues once more about his long-term durability. Although Vick appears fine short term, the Eagles’ backup QB spot is one of the few remaining positions that needs sorting out. Foles completed 6-of-10 passes for 144 yards and two long TD passes — 70 yards to Damaris Johnson and 44 to Mardy Gilyard — both on well-placed balls. But that’s one performance against a third-team Steelers defense, so perspective is needed. Kafka, the favorite to win the backup spot, had a rough game and hasn’t exactly run away with the job to date. Kafka will miss a few weeks of practice time but still could claim the backup job because of his experience and knowledge of the offense and if Foles takes a step back.