I feel that in discussing this game's cooperative nature, and whether or not said nature will remain in place, we may be overlooking another crucial element that may have contributed to the release's being pushed back: the breadth of the Star Wars canon itself, specifically the Expanded Universe.
Star Wars: The Card Game, as it was presented at Gen Con, focused solely on the Galactic Civil War. Indeed, for many fans this is the crux of the story: a band of unlikely heroes battling a seemingly impossible battle against the superior might of the Emperor's minions. It's iconic enough to stand on its own. And yet, for many others, myself included, this is not the end, nor the beginning, of the epic saga that is Star Wars. And for a game to have such an all-encompassing name as Star Wars: The Card Game, it should embrace all facets of the franchise, not just those that are considered to be the defining portion. In other words, I believe that a consideration for Expanded Universe lore may have impacted the release date, since various elements of play tied the Gen Con prototype intrinsically to the Classic Era. thereby making it inappropriate for a game with a broader scope.
As I have stated in a previous thread, I do believe that FFG's choice of founding their game on the Classic Era was the right decision for the time, as there's been a decided lack of attention to the Original Trilogy in the recent decade (with the exception of multiple DVD/BD releases). But by removing the game's artificial restriction to this four-year pinprick in the roughly 5,000-year span of heavily documented lore, the company would leave itself vastly more room for future expansion on this game without branching into others, and because it's an LCG, it'd be easy enough for purists to skip the packs and expansions that don't fit their vision of what Star Wars means to them.
My take: Instead of Rebel and Imperial cards, sets should be divided into Light Side and Dark Side cards (and perhaps Neutral cards), with players being restricted to one side or the other when building decks, and perhaps there could even be a small era symbol designating a card's position in the Star Wars continuity, in order that players who dislike anachronism may conveniently avoid it in their deckbuilding. Depending on how the gameplay itself is set up - namely, whether or not a direct and crucial relationship between the two sides of the Force will exist, as there was in the two most well-known previous iterations of the license - there may not even be a need to maintain decks of both sides and mutually select from the pair at the start of each game, though I expect such a rule would be put in place for official events anyway. (This part assumes that there will be a PvP mode at all, which IMO is a fair assumption given the premise on which I'm basing this topic, that the game ought to encompass everything Star Wars, which certainly includes the idea of two players representing the two sides of the Force in opposition.)