Barry Allen will still be making his first appearance in Arrow episodes 8 and 9 before donning his iconic costume in his pilot. According to Deadline, The CW execs were so impressed with the character in those episodes they made the call to move his first appearance as a superhero from a late-in-the-season Arrow episode to his own official debut. Not only is this a major vote of confidence in the show, but pilots get much bigger budgets than regular episodes — which the "back-door pilot" would have obviously been one of — so this is very good news all-around.